Hello

So, a few days ago I had a problem (for the second time) with Steam: it stopped recognizing the game as installed on my computer. I was able to play it for 2 days, launching directly from the folder where it was installed (without Steam), but somehow it stopped working. I started to get a message saying that I HAD TO launch through Steam (why??). I was forced to redownload everything, and I did. It finished this morning. Steam was recognizing it and everything looked fine, but when I open the launcher, it wants to download everything again, but it's already installed! What's going on? This is really stressing me out. I looked for some solutions and I'm repairing the launcher, but it's downloading more than 50 GB anyway, so...
Why does this happen? Why can't we launch outside of Steam? I hope you work on solutions to prevent these problems from happening again, it's really annoying

Thank you