Hi @Laska,
The keyboard driver for the Pro1 has been completely rewritten by @tdm when he did the original port of LineageOS.
The keymap file in LOS 16 is located in /sys/bus/i2c/drivers/aw9523b/6-0058/keymap. However, any changes to that file are not persistent across reboots.
If you have root, the easiest way to make changes persistent is the following:
Install the app Run Userinit from F-Droid. Execute Run-Userinit once and grant it root privilege.
Next, place your modified keymap e.g. in /data/system/keyboard/keymap (you may have to create the "keyboard" folder