The safest and most reliable repository for Assetto Corsa mods is RaceDepartment. It is the gold standard for quality control. If you download a car or track from here, you are guaranteed it has been scanned for malware and tested for quality.
To understand the mods, you must understand the version. Assetto Corsa’s development history is divided primarily between Kunos Simulazioni (the original developers) and the subsequent stewardship by Digital Bros/505 Games.
High-end mods, such as highly detailed drift cars (e.g., the Death Wish Garage or World Drift Tour packs) or hyper-realistic tracks, are often not hosted on public sites. assetto corsa 1164 mods link
Do not use the vanilla Assetto Corsa launcher. It will crumble under 1,164 mods. You need Content Manager, a free (donation-based) third-party launcher.
The non-profit Internet Archive (archive.org) has several uploads titled assetto_corsa_1164_mods_collection. These are legal to download because they link back to original free sources. Search for: The safest and most reliable repository for Assetto
"assetto corsa 1164" archive.org
Red flags to avoid:
You cannot discuss mods for Assetto Corsa without mentioning the software that actually makes them work. If you are on version 1.16.4, these tools are mandatory for a modern experience.