Companion to the bans piece, but centred on the scenes themselves instead of the ban question.

Singleplayer modding

Add-on atmospheres. Interior customisations. Lore expansions. Texture packs. Car substitutions. Largely enthusiast-driven.

Tolerated by Rockstar. Gradually increasing playerbase. These are the mods reviewers will talk about.

Online / multiplayer modding

Custom server architectures (FiveM, RAGE MP). Roleplay scenes. Creation of custom gamemodes. Huge community. Frequently business-oriented - servers make money from players.

Tolerated by Rockstar as a framework (FiveM purchased). Vigorously prosecuted when used for cheating.