I’m not up to date on hardware, so I’ll refrain from recommending specific components. I went with AMD Ryzen CPU and Nvidia GPU (using closed source driver) last time I upgraded my PC and it usually works fine, though I know many recommend AMD GPUs nowadays for Linux. If €1000 is your total budget, it might be worth considering a second hand GPU. For example a used RTX 3080 goes for around €300 and they are still quite capable, though someone else will have to say if that’s enough for the flight sims.
One thing you might want to look up is if the game uses hardware raytracing, and if that works on Linux. Out of the games I play, World of Warships looks worse for me than what I see on youtube, despite that I have set all graphics settings to max. Maybe it’s possible to fix by configuring Wine/Proton/DXVK etc. I haven’t really looked into it, but just so you’re aware of potential issues.
I used this list for help when choosing a power supply, but I think that becomes more important if you buy a high end GPU.
I use Steam for almost all my gaming, and it makes running (most) Windows games a breeze.
Still are, but I guess a lot of people don’t know much about them