Sometimes there are spikes in this issue being reported and it usually coincides with a game update or macOS update. Game updates can render CC/Mods incompatible so you need to check with the creator that the content you use has been updated to work with the current patch level of the game. When macOS updates are applied this can sometimes change iCloud Drive settings if dialogue windows ask the user to confirm new actions so check the location of your Documents folder in System Preferences.

1. Are CC and Mods enabled in your game options? If not enable them and restart the game.
2. Is your game fully patched up to date?
3. Are the CC and Mods you’re trying to use fully compatible with the latest version of the game? Check on the creator’s website that they are. The good creators will always check their content is compatible after an update and release an updated version if necessary or possible. Check the SimsVIP broken Mods page for updated lists after each patch.
4. Are the CC/Mods definitely for Sims 4 and not Sims 1, 2 or 3?
5. Have you unzipped the downloaded CC/Mods so you are only placing .package and/or .ts4script files in your Mods folder?
6. Do you have iCloud Drive enabled to store your Documents folder in the cloud? If your Mac internal storage is getting full and Optimise Mac Storage is enabled, it will automatically push files to the cloud.
7. Have you tried repairing your game? Right click on the game in your Origin games library and select repair game.

ItsaprilXD’s fabulous guide to installing CC/Mods on a Mac is also worth a read.