Use the arduino-cli board details command:
$ arduino-cli board details --fqbn megaTinyCore:megaavr:atxy6
Board name: ATtiny3226/3216/1626/1616/1606/826/816/806/426/416/406
FQBN: megaTinyCore:megaavr:atxy6
Board version: 2.6.8
Identification properties: board=atxy6
Package name: megaTinyCore
Package maintainer: Spence Konde
Package URL: http://drazzy.com/package_drazzy.com_index.json
Package website: https://github.com/SpenceKonde/megaTinyCore
Platform name: megaTinyCore
Platform category: Contributed
Platform architecture: megaavr
Platform URL: https://SpenceKonde.github.io/megaTinyCore/megaTinyCore-2.6.8.tar.bz2
Platform file name: megaTinyCore-2.6.8.tar.bz2
Platform size (bytes): 827571
Platform checksum: SHA-256:33c6c68f5f5dfff1de02113c968ad08dabc2cedddd78b1f9b004d91e0183de9f
Required tool: DxCore:avr-gcc 7.3.0-atmel3.6.1-azduino6
Required tool: DxCore:avrdude 6.3.0-arduino17or18
Required tool: arduino:arduinoOTA 1.3.0
Required tool: megaTinyCore:python3 3.7.2-post1
Option: Chip chip
ATtiny3226 ✔ chip=3226
ATtiny3216 chip=3216
ATtiny1626 chip=1626
ATtiny1616 chip=1616
ATtiny1606 chip=1606
ATtiny826 chip=826
ATtiny816 chip=816
ATtiny806 chip=806
ATtiny426 chip=426
ATtiny416 chip=416
ATtiny406 chip=406
Option: Clock clock
20 MHz internal ✔ clock=20internal
16 MHz internal clock=16internal
10 MHz internal clock=10internal
8 MHz internal clock=8internal
5 MHz internal clock=5internal
4 MHz internal clock=4internal
2 MHz internal clock=2internal
1 MHz internal clock=1internal
20 MHz internal - tuned clock=20internaltuned
16 MHz internal - tuned clock=16internaltuned
12 MHz internal - tuned clock=12internaltuned
10 MHz internal - tuned clock=10internaltuned
8 MHz internal - tuned clock=8internaltuned
6 MHz internal - tuned clock=6internaltuned
5 MHz internal - tuned clock=5internaltuned
4 MHz internal - tuned clock=4internaltuned
1 MHz internal - tuned clock=1internaltuned
20 MHz external clock clock=20extclock
16 MHz external clock clock=16extclock
12 MHz external clock clock=12extclock
10 MHz external clock clock=10extclock
8 MHz external clock clock=8extclock
24 MHz internal - tuned, overclocked clock=24internaltuned
25 MHz internal - tuned, overclocked clock=25internaltuned
30 MHz internal - tuned, overclocked, may be unstable, req. 20 MHz fuse clock=30internaltuned
32 MHz internal - tuned, 2-series, overclocked, may be unstable, req. 20 MHz fuse clock=32internaltuned
24 MHz external clock - overclocked clock=24extclock
25 MHz external clock - overclocked clock=25extclock
30 MHz external clock - overclocked, may be unstable clock=30extclock
32 MHz external clock - overclocked, may be unstable clock=32extclock
Option: millis()/micros() Timer millis
Enabled (default timer) ✔ millis=enabled
Disabled (saves flash) millis=disabled
TCA0 (default on 0-series) millis=timera
TCD0 (1-series only, default there) millis=timerd
TCB0 (breaks tone() and Servo) millis=timerb0
TCB1 (3216, 1616, 2-series only) millis=timerb1
RTC (no micros) millis=rtc
RTC w/w32.768 kHz ext. crystal (1/2-series only, no micros) millis=rtcxtal
RTC w/w32.768 kHz ext. oscillator (1/2-series only, no micros) millis=rtcxosc
Option: Startup Time startuptime
8ms ✔ startuptime=8
0ms startuptime=0
1ms startuptime=1
2ms startuptime=2
4ms startuptime=4
16ms startuptime=16
32ms startuptime=32
64ms startuptime=64
Option: BOD Voltage Level (burn bootloader req'd) bodvoltage
1.8V (5 MHz or less) ✔ bodvoltage=1v8
2.6V (10 MHz or less) bodvoltage=2v6
4.2V (20 MHZ or less) bodvoltage=4v2
2.1V (Unofficial) bodvoltage=2v1
2.9V (Unofficial) bodvoltage=2v9
3.3V (Unofficial) bodvoltage=3v3
3.7V (Unofficial) bodvoltage=3v7
4.0V (Unofficial) bodvoltage=4v0
Option: BOD Mode when Active/Sleeping (burn bootloader req'd) bodmode
Disabled/Disabled ✔ bodmode=disabled
Enabled/Enabled bodmode=enabled
Enabled/Sampled (1 kHz) bodmode=ensampfast
Enabled/Sampled (125 Hz) bodmode=ensampslow
Sampled/Sampled (1 kHz) bodmode=sampledfast
Sampled/Sampled (125 Hz) bodmode=sampledslow
Sampled/Disabled (1 kHz) bodmode=sampdisfast
Sampled/Disabled (125 Hz) bodmode=sampdisslow
Enabled hold wakeup/Disabled bodmode=endisholdwake
Option: Save EEPROM (burn bootloader req'd) eesave
EEPROM retained ✔ eesave=enable
EEPROM not retained eesave=disable
Option: UPDI/Reset Pin Function (burn bootloader req'd) resetpin
UPDI (no reset pin) ✔ resetpin=UPDI
UPDI w/reset on PB4 (2-series only) resetpin=UPDIaltrst
Option: printf() printf
Default (doesn't print floats, 1.4k flash use) ✔ printf=default
Full, 2.6k, prints floats printf=full
Minimal, 1.1k flash used printf=minimal
Option: Wire (Wire.h/I2C) Library mode wiremode
Master or Slave (saves flash and RAM) ✔ wiremode=mors
Master and Slave wiremode=mands
Option: WDT timeout (burn bootloader req'd. Cannot be disabled at runtime if set here) WDTtimeout
Disabled (recommended) ✔ WDTtimeout=disabled
Window remains open for 8 Seconds WDTtimeout=8seconds
Window remains open for 4 Seconds WDTtimeout=4seconds
Window remains open for 2 Seconds WDTtimeout=2seconds
Window remains open for 1 Second WDTtimeout=1second
Window remains open for 500 milliseconds WDTtimeout=500msec
Window remains open for 250 milliseconds WDTtimeout=250msec
Window remains open for 125 milliseconds WDTtimeout=125msec
Option: WDT window (if desired. burn bootloader req'd. Cannot be disabled at runtime if set here) WDTwindow
No delay before window "opens" ✔ WDTwindow=disabled
8 Second before window "opens" WDTwindow=8seconds
4 Second before window "opens" WDTwindow=4seconds
2 Second before window "opens" WDTwindow=2seconds
1 Second before window "opens" WDTwindow=1second
500 millisecond before window "opens" WDTwindow=500msec
250 millisecond before window "opens" WDTwindow=250msec
125 millisecond before window "opens" WDTwindow=125msec
62.5 millisecond before window "opens" WDTwindow=63msec
Option: PWM pins (advanced, see core documentation) PWMmux
PB0-2, PA3-5, 1-series: PC0/1 (default) ✔ PWMmux=A_default
PB0-2, PA3-5. No TCD PWM even on 1-series. PWMmux=default
PB0-2 (buffered), 1-series: PC0/1 PWMmux=A_buffered
PB0-2 (buffered), 1-series: PA4/5 PWMmux=D_buffered
PB0-2 (buffered). No TCD PWM even on 1-series. PWMmux=buffered
PB0,1,5, PA3-5, 1-series: PC0/1 PWMmux=U6_A
PB0,1,5, PA3-5. No TCD PWM even on 1-series. PWMmux=U6
PB0,1,5 (buffered), 1-series: PA4/5 PWMmux=U3_D
PB0,1,5 (buffered), 1-series: PC0/1 PWMmux=U3_A
PB0,1,5 (buffered). No TCD PWM even on 1-series. PWMmux=U3
PB3-5 PA3-5, 1-series: PC0/1 PWMmux=I6_A
PB3-5, PA3-5. No TCD PWM even on 1-series. PWMmux=I6
PB3-5 (buffered), 1-series: PA4/5 PWMmux=I3_D
PB3-5 (buffered), 1-series: PC0/1 PWMmux=I3_A
PB3-5 (buffered). No TCD PWM even on 1-series. PWMmux=I3
PB3-5, PC3, PA4/5, 1-series: PC0/1 PWMmux=SC6_A
PB3-5, PC3, PA4/5. No TCD PWM even on 1-series. PWMmux=SC6
Option: attachInterrupt Mode attach
On all pins, with new implementation. ✔ attach=allenabled
Only enabled ports attach=manual
Old version, (may fix bugs) attach=oldversion
Programmers: ID Name
serialupdi SerialUPDI - 230400 baud
serialupdi460k SerialUPDI - FAST: 4.5v+ 460800 baud (CH340 - and maybe some others)
medbg Xplained Mini (mEDBG, debug chip: ATmega32u4)
nedbg Curiosity Nano (nEDBG, debug chip: ATSAMD21E18)
edbg Xplained Pro (EDBG, debug chip: AT32UC3A4256)
serialupdi57k SerialUPDI - SLOW: 57600 baud
serialupdi921k_wd1 SerialUPDI - TURBO: 4.5v+ 921600 baud w/write delay, (adapters that support it and are not CH340, many fall back to 115200)
jtag2updi jtag2updi
snap_updi MPLAB SNAP (UPDI mode)
pickit4_updi PICkit4 (UPDI mode)
atmelice_updi Atmel-ICE
serialupdi921k SerialUPDI - TURBO: 4.5v+ 921600 baud (CH340 (and maybe some others) only)
serialupdi230k_wd1 SerialUPDI - 230400 baud w/write delay, 2.7V+ (Linux/MacOS: other adapters, Win: maybe some adapters)
serialupdi460k_wd1 SerialUPDI - FAST: 4.5v+ 460800 baud w/write delay (other non-CH340 adapters, often slower than 230k, esp. on Windows)
With atmega's it is really simple because you don't have to set any arguments at al. You just specify that you are using a nano or uno and you're good.
marks also anwsers my 2nd question, what options must one set. 