OK, I did find some Optiboot bootloader files in this directory
C:\Users\My name\AppData\Local\Arduino15\packages\arduino-tiny-841\hardware\avr
Not sure which one to use. I tried this one: optiboot_attiny841at8.hex and the Arduino showed a few Hashes ### to show that it was programming the Tiny841 but still had some errors. The red light now blinks twice quickly then off for a second or so.
avrdude: Version 6.3, compiled on Dec 16 2016 at 13:33:19
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2014 Joerg Wunsch
System wide configuration file is "C:\Users\Fergus Dixon\AppData\Local\Arduino15\packages\arduino-tiny-841\hardware\avr\1.0.6/avrdude.conf"
Using Port : COM2
Using Programmer : arduino
Overriding Baud Rate : 57600
Setting bit clk period : 5.0
AVR Part : ATtiny841
Chip Erase delay : 15000 us
PAGEL : P00
BS2 : P00
RESET disposition : possible i/o
RETRY pulse : SCK
serial program mode : yes
parallel program mode : yes
Timeout : 200
StabDelay : 100
CmdexeDelay : 25
SyncLoops : 32
ByteDelay : 0
PollIndex : 3
PollValue : 0x53
Memory Detail :
Block Poll Page Polled
Memory Type Mode Delay Size Indx Paged Size Size #Pages MinW MaxW ReadBack
eeprom 65 6 4 0 no 512 4 0 4000 4500 0xff 0xff
flash 65 12 32 0 yes 8192 16 512 4500 4500 0xff 0xff
signature 0 0 0 0 no 3 0 0 0 0 0x00 0x00
lock 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
lfuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
hfuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
efuse 0 0 0 0 no 1 0 0 9000 9000 0x00 0x00
calibration 0 0 0 0 no 1 0 0 0 0 0x00 0x00
Programmer Type : Arduino
Description : Arduino
Hardware Version: 3
Firmware Version: 6.2
Vtarget : 0.3 V
Varef : 0.3 V
Oscillator : 28.800 kHz
SCK period : 3.3 us
avrdude: AVR device initialized and ready to accept instructions
Reading | ################################################## | 100% 0.01s
avrdude: Device signature = 0x1e9315 (probably t841)
avrdude: reading input file "C:\tmp\arduino_build_628908/Blink.ino.hex"
avrdude: writing flash (920 bytes):
Writing | ################################################## | 100% 1.85s
avrdude: 920 bytes of flash written
avrdude: verifying flash memory against C:\tmp\arduino_build_628908/Blink.ino.hex:
avrdude: load data flash data from input file C:\tmp\arduino_build_628908/Blink.ino.hex:
avrdude: input file C:\tmp\arduino_build_628908/Blink.ino.hex contains 920 bytes
avrdude: reading on-chip flash data:
Reading | ################################################## | 100% 1.85s
avrdude: verifying ...
avrdude: verification error, first mismatch at byte 0x0002
0xff != 0x3d
avrdude: verification error; content mismatch
avrdude done. Thank you.
the selected serial port
does not exist or your board is not connected