A bit of both, really.
I’ve never tried to run Linux on a machine with an NVIDIA GPU, or on a machine with two GPUs. But from what I have read, this is the impression that I get:
It’s quite common to have a bit of trouble getting anything working, and you will run into problems far more often than with any other brand of GPU (which will just work perfectly).
Many things won’t work with the proprietary drivers, because they implement everything their own way, and so software has to be written against the NVIDIA proprietary drivers, rather than using the standard tools that everything else uses like OpenGL and Mesa.
https://arstechnica.com/gadgets/2020/04/linux-on-laptops-asu... is the sort of thing I’ve heard of: there, the NVIDIA GPU is trouble from start to end. Admittedly it might have gone more smoothly with something other than Ubuntu, with more recent versions of kernels and other such stuff (I like Arch, so this wouldn’t be a problem for me), but it’s still just bad.
But then too, I mentioned Wayland: because of how NVIDIA made their own world on Linux, the proprietary drivers are completely incompatible with Wayland—basically NVIDIA hardcoded support for X (again, rather than using the standard approach everyone else settled on) and haven’t done so for Wayland.
If you use Nouveau instead of the proprietary drivers, you’re left with a GPU missing a substantial fraction of its functionality, stuck at a low clock speed in power-draining mode. But I think you might be able to use Wayland.
I gather that Linux has problems in any dual GPU environment, but that the issues are far worse with NVIDIA than with anything else. If you’re operating a single-GPU machine and are content to use the proprietary drivers, I gather it’s not such a problem, though many applications may be unable to use GPU acceleration.
I welcome any corrections to what I’ve written here. As I say, this is all just hearsay.