I can't see the district or the new improvement they are replaced with a red !

I just tried to replicate this on every version of the game, and it's working fine for me.

What operating system are you on, and do you happen to be subscribed to the old version of the civilization?

I'm on windows and no I'm not sub to the last version of this civ

Hmm... Have you tried running the game with only the CIVITAS Sassanid and CIVITAS Kawad I mods active to rule out any mod conflicts?

Can you please navigate to Documents\My Games\Sid Meier's Civilization VI\Logs and share the contents of the Modding and Database logs, then share them on Pastebin?

Doesn't work even without any other mod

Here are the things you asked for:

DataBase: https://pastebin.com/tPJwj1SS

Modding: https://pastebin.com/gtwfcwMc

Thanks. What build does it say in the bottom left of your game screen? Should be something like 1.0.x.x (xxxxxx).

1.0.0.290 (405094)

Thought that might be the case. Looks like you're out of date. You're missing 4 updates. You want 1.0.0.341. I'm not 100% sure whether that has anything to do with the art not working, but it's definitely causing some database issues with the mod.

Do you know a way to update civ6 if you cracked it ? (It's for a friend)

Haha. Unfortunately, I don't have any experience there.

Ok nevermind and thanks anyway