I'm playing TS4 on Windows 10. The game opens and runs just fine. All of my CAS and buy/build mode CC works just fine. There are no issues with .package files. It's purely an issue with script mods.

The Problem:
So, I start up the game as usual. I open Game Options. I go to 'other.' The box for 'allow custom content' is already checked, but the box to allow script mods is not. So I check the box to allow script mods, hit 'apply changes,' and exit to desktop. I reopen the game, go to game options and other, and...the box to allow script mods is not checked. I check it again, apply changes, and exit game. I reopen it. Once again, the box to allow script mods is not checked.

You see the pattern here, I'm sure. I've been through this like a dozen times now and it's rapidly running through my patience. I only have a few script mods, so is it a problem with one of them specifically? They're an Imaginative Trait, the AOM Selectable Pets mod, the Slice of Life mod, and TwistedMexi's AllCheats mod.

Close your game
go into your Sims 4 folder (the one in Documents) and open the Options.ini file in Notepad
look for the line scriptmodsenabled, change the 0 to 1, so it's scriptmodsenabled = 1
save the file and reopen your game, script mods should be enabled now

I believe this issue is unrelated to mods, but anyways, this is how you work around it.

Well, that fixed it, in a...roundabout sort of way. Turns out my Options.ini file was broken. Which I guess isn't surprising, since the last update seemed to break everything. I had to toss it into a different folder and let the game generate a new one.