There are the steps that I used to activate the mod in a Ubuntu version, using the Proton 9.4 version.

Option 1:

1- Subscribe to the 3 mods
2- Open the game, go to mod selector and activate and sort all the mods
3- Go to the folder ~/snap/steam/common/.steam/steam/steamapps/common/Total War Rome II
4- Open the file "used_mods.txt" and copy all the text
5- Go to the folder ~/snap/steam/common/.local/share/Steam/steamapps/compatdata/214950/pfx/drive_c/users/steamuser/AppData/Roaming/The Creative Assembly/Rome2/scripts
6- Open the file "preferences.script.txt"
7- At the end of the file paste all the data and save

Please check that the last command in the "preferences.script.txt" finish with a ;

All the lines must to finish with a ";" If you don't add a ; at the finish of the command, once the you will start the game, the game will restore the file to the original version and you will not be able to start the game .

Option 2:

1- Subscribe to the 3 mods
2- Open the game, go to mod selector and activate and sort all the mods
3- Go to the folder ~/snap/steam/common/.steam/steam/steamapps/common/Total War Rome II
4- Open the file "used_mods.txt" and copy all the text
5- Go to the folder ~/snap/steam/common/.local/share/Steam/steamapps/compatdata/214950/pfx/drive_c/users/steamuser/AppData/Roaming/The Creative Assembly/Rome2/scripts
6- Copy the file "preferences.script.txt" in a new file with the name "preferences.script.bcp"
7- Open the file "preferences.script.bcp"
8- At the end of the file paste all the data and save
9- Create a file in the folder that you want with the extension .sh with the following text:

#!/bin/bash
cp ~/snap/steam/common/.local/share/Steam/steamapps/compatdata/214950/pfx/drive_c/users/steamuser/AppData/Roaming/"The Creative Assembly"/Rome2/scripts/preferences.script.bck ~/snap/steam/common/.local/share/Steam/steamapps/compatdata/214950/pfx/drive_c/users/steamuser/AppData/Roaming/"The Creative Assembly"/Rome2/scripts/preferences.script.txt


10- Make it as an executable: chmod +x Scriptname.sh
11- Execute it always before to start the game because sometimes the preferences.script.txt returns to the original state



I hope this guide will help you.