Does anyone have the adb commands to activate button mapper on the lg exalt

No. But probably it's not specifically for LG Exalt.
Probably it's for all phones.
And yes, I would also want to know.
I know that you have to give a command to grant accessibility access, but don't know the excact command.
maybe someone could help?

This worked for me

A-settings put secure enabled_accessibility_services com.android.cts.flar2.homebutton/a.i:com.android.cts.io.github.virresh.matvt
B-settings put secure accessibility_enabled 1

how do u add a button in button mapper, when i click the "add" after i select my desired button it selects my middle button because i clicked it.

LKWDBochur use voice access to click ok. Or u can use scrscpy.

Btw on the phones I tried the Button mapper, it didn't show an accessibility error (because I granted accessibility access) but when set something it plain didn't work, it didn't change anything.
Does someone maybe know what I keep doing wrong?