[2021] Since last update my game regularly crashes after few minutes - massive performance issues with Dx12

Hello,

I've been dying to try out this new DLC as usual with my friends. After you finally fixed some of the problems we could start playing after a few days. Or so we thought. For some reason, my game crashes a few minutes after we start. Between 5 and 30 minutes. And not only my game, no, my whole computer restarts.
This obviously has never happened before this DLC.
I tried a few different things. Updated drivers, switched to directx 12...nothing works. Actually, directx12 doesn't even work for me anymore. The game lags very much with directx12, even in the main menu it's almost impossible to navigate.
Before you ask: Yes, my drivers are up to date, yes, my PC is able to play this game, I have played over 250 hours on highest graphics level since release. And yes, I have gone through the usual bugfixes, so please don't just link me the standard troubleshooting website. I have done all of those!
When the game crashes, there is a green screen for a second or so, afterwards my PC restarts. This issue only occurs in Anno1800. It doesn't happen in Warzone, it doesn't happen in Europa Universalis 4, it doesn't happen in any other game.