My Script Mods show up at startup but my custom content doesn't.

the Mod conflict detector detects errors between mods. Not between Mods/CC and the game. If the CC is not listed at the beginning at the game along with your Mods then they are not installed properly. A common error is that they are in a compressed format such as zip in which case they need to be unpacked.

I've played the game before with the same custom content, but I downloaded the road to fame mod and then they disappeared from the list. When I uninstalled the road to fame mod it didn't fix it.

I'm having the same issue. I had downloaded Sims 4 to a new computer slightly after the Get Famous (trailer) was released (I haven't moved my old game files over yet). MCCC will show up in the mods/cc pop-up when I start the game, but nothing else will. I tried uninstalling an reinstalling, repairing the game, taking cc out of subfolders, and doing what was recommended in the previous suggestion on this board, even putting a single cc item in (without mccc). None of this has worked, and I have been having this issue since I first attempted to use cc on this new computer.

Get Famous has not been released yet. Comes next week.

Likely your CC came in a compressed format such as ZIP or RAR and you haven't unpacked it.

I meant the Get Famous Trailer... that was a typo i didnt catch...

as for the cc format, most of them are package files

If they don't show up in the dialog when starting the game then they are not in the correct folder.

Here is an easy way to find out which folder your game is using: https://sims4.crinrict.com/en/2018/07/how-to-find-your-user-folder/

I had it in the mods folder. I have fixed the issue by reinstalling one of my cc items (a hairstyle) and placing it in my game. everything worked as usual so i continued to put the cc in the folder in small chunks of about 15 items and then loading up the game. Everything works fine now somehow.