You might say I have a few installed 
:
$ arduino-cli core list
ID Installed Latest Name
adafruit:samd 1.7.10 1.7.10 Adafruit SAMD Boards
TeeOnArdu:avr 1.0.3 1.0.3 Adafruit TeeOnArdu
adafruit:wiced 0.6.6 0.6.6 Adafruit WICED
arduino:avr 1.8.5 1.8.5 Arduino AVR Boards
arduino:mbed_edge 3.1.1 3.1.1 Arduino Mbed OS Edge Boards
arduino:mbed_nano 3.1.1 3.1.1 Arduino Mbed OS Nano Boards
arduino:mbed_nicla 3.1.1 3.1.1 Arduino Mbed OS Nicla Boards
arduino:mbed_portenta 3.1.1 3.1.1 Arduino Mbed OS Portenta Boards
arduino:mbed_rp2040 3.1.1 3.1.1 Arduino Mbed OS RP2040 Boards
arduino:megaavr 1.8.7 1.8.7 Arduino megaAVR Boards
arduino:nrf52 1.0.2 1.0.2 Arduino nRF52 Boards
arduino:samd 1.8.13 1.8.13 Arduino SAMD Boards (32-bits ARM Cortex-M0+)
Arrow:samd 2.1.0 2.1.0 Arrow Boards
atmel-avr-xminis:avr 0.6.0 0.6.0 Atmel AVR Xplained-minis
ATTinyCore:avr 1.5.2 1.5.2 ATTinyCore
Balanduino:avr 1.2.0 1.2.0 Balanduino
bitDuino10-aTPI:avr 1.0.0 1.0.0 bitDuino10-arduinoTPI
digistump:avr 1.7.5 1.7.5 Digistump AVR Boards
DxCore:megaavr 1.4.7 1.4.7 DxCore
electroniccats:mbed 1.0.5 1.0.5 Electronic Cats Mbed OS Boards
electroniccats:samd 2.0.7 2.0.7 Electronic Cats SAMD(L)(C) Core for Arduino
emoro:avr 3.2.2 3.2.2 EMORO 2560
esp32:esp32 2.0.3 2.0.3 ESP32 Arduino
esp8266:esp8266 3.0.1 3.0.1 esp8266
industruino:samd 1.0.1 1.0.1 Industruino SAMD Boards (32-bits ARM Cortex-M0+)
Intel:arc32 2.2.0 2.2.0 Intel Curie Boards
Intel:i686 1.6.7+1.0 1.6.7+1.0 Intel i686 Boards
LGT8fx Boards:avr 1.0.6 1.0.6 LGT8fx Boards
littleBits:avr 1.0.0 1.0.0 littleBits Arduino AVR Modules
m5stack:esp32 2.0.2 2.0.2 M5Stack
Maixduino:k210 0.3.11 0.3.11 Maixduino(k210)
MattairTech_Arduino:samd 1.6.18-beta-b1 1.6.18-beta-b1 MattairTech SAM D|L|C core for Arduino - Beta build
MegaCore:avr 2.1.3 2.1.3 MegaCore
megaTinyCore:megaavr 2.5.10 2.5.10 megaTinyCore
microUPDIcore:avr 1.0.2 1.0.2 microUPDI Firmware Uploader
MightyCore:avr 2.1.3 2.1.3 MightyCore
MiniCore:avr 2.1.3 2.1.3 MiniCore
sandeepmistry:nRF5 0.7.0 0.7.0 Nordic Semiconductor nRF5 Boards
OpenCM904:OpenCM904 1.5.0 1.5.0 OpenCM9.04
opentracker:sam 1.0.5 1.0.5 OpenTracker ARM (32-bits) Boards
realtek:AmebaD 3.1.1 3.1.1 Realtek Ameba Boards (32-bits ARM Cortex-M33 @200MHz)
RedBear:nRF51822 1.0.8 1.0.8 RedBear nRF51822 Boards (32-bits ARM Cortex-M0)
RedBear:nRF52832 0.0.2 0.0.2 RedBear nRF52832 Boards (32-bits ARM Cortex-M4F)
Sanguino:avr 1.0.3 1.0.3 Sanguino
Seeeduino:samd 1.8.2 1.8.2 Seeed SAMD Boards
Seeeduino:rp2040 1.9.3 1.9.3 Seeed XIAO RP2040
SparkFun:apollo3 2.1.1 2.1.1 SparkFun Apollo3 Boards
STMicroelectronics:stm32 2.2.0 2.2.0 STM32 MCU based boards
sduino:stm8 0.5.0 0.5.0 STM8S Boards
teensy:avr 1.56.1 1.56.1 Teensy
TL7788:arm 1.0.3 1.0.3 TL7788 Boards
Only the one you saw mentioned on the GitHub issue:
https://github.com/arduino/arduino-ide/issues/714#issuecomment-1114452951
In the mean-time: a workaround for those who want to be able to comfortably work in the editor:
- Press CTRL+SHIFT+P
- Type "server" in the search field
- Click "Arduino: Stop Language Server"
- Enjoy working in a super-responsive IDE with lightning-fast suggestions
- When ready to re-index, select the "Arduino: Start Language Server" command and wait for a re-index