Further to the queries I’ve received recently about flickering depth effects in TS3, I explained it’s because of anti-cheat detection in online games that often think ReShade’s depth buffer integration is cheat software and can ban people for using it, so ReShade introduced a feature quite some time ago where if it detects calls to a game server it disconnects the depth buffer.
Obviously using ReShade in any of The Sims games doesn’t result in EA banning anyone, so you don’t need to worry about that, but ReShade doesn’t understand that TS3 isn’t an online competitive game, and so disconnects the depth buffer just like it would if you were using it in any other game, because the TS3 store is always online and makes those constant calls to the server.
One solution is to disconnect from the internet while you’re playing TS3.
I mentioned there was an alternative version of ReShade 5 that disables this anti-cheat protection, but I wasn’t sure if it was still available. I’ve checked, and I believe what you want is the version that says ‘Full Add-on Support’ from the official download here.
Of course, if you choose to use that version in an online competitive game you take full responsibility if your account gets banned. But for TS3 (or any other Sims game) you’ll be absolutely fine. Here’s a forum post by ReShade’s developer explaining the difference between the two versions.