If I were buying right now, I’d be getting the 7900XTX, and that would be for using on a 4k monitor.
The cards trade blows in testing, but the 7900XTX generally edges out in rasterized performance. Plus you get a lot more VRAM. The 4080 would do better in ray tracing, but that doesn’t apply unless you have other games you want to utilize it on (none in MSFS). It would likely do better for VR, but doesn’t sound like you’re using that. It has DLSS, but you could probably get by with no upscaling on either card (I run my 6600XT at 1440p fine with no FSR upscaling). It has frame generation, but I think that’s almost useless on a slow paced game/sim like this.
In short, I wouldn’t go with Nvidia unless you have a specific need to use their cards. If you’re not sure, then you probably don’t have a real need for it.