Main Menu -> Mods -> Open Mod Folder sets globals.modfolder
icon = globals.modfolder + "/Gatreex/Images/dagger.png",
Viewing post in Adding new items or images
https://itch.io/board/252654/portarits-packs.
There is a portrait packs section as well as a mods section.
The Debug mod is not applied through the mod system. It is a manual patch.
Also, beware changing which mods are applied as every time you apply the changes you will reset all of the scripts in the Strive program folder.
I recommend not using "%appdata%" in paths as it is not compatible with all OS and computers. If it's only for you then there may not be problems, but "user://mods" will be more broadly compatible.
The game has a guide that explains how the mod system works, which is found in the Help section of the Mods menu. There is also a slightly outdated copy of the guide in the wiki.