Suggestions:
1. Don't run any file system checking or repair tools untill you've manually checked and you're sure the files are broken/missing. Some of those tools can be a chainsaw unless you're familiar.
2. Take a look in \Steam\steamapps\common\assettocorsa\apps (or wherever that is for you). There should be two folders "lua" and "python".
3. Check if the missing apps actually still have files/folders in there.
4. They are, restart Content Manager and in "miscellaneous | PYTHON APPS" and "miscellaneous | LUA APPS", check if they're listed there.
5. Some apps install as mods, so also check "mods" if they're available or enabled (like Nuzzis stuff)
6. If it's all gone, you might have to get comfortable with chkdsk and it's options, or live dangerously and just re-install the missing apps?