Those 2 games are extremely solid in my experience, haven’t had a crash ever in either of them.
I’ve played Borderlands 2 for 744 hours over many years with different hardware without a problem, except that I can’t get SHiFT keys to work in the Linux version, so if I want to use SHiFT, I switch to Proton for that. Both work flawlessly otherwise. I have only tried Portal native though.
I’m currently using the Manjaro distro with an old Ryzen 5 1600 CPU, Radeon RX 6800 XT GPU, and 16 Gig Ram.
My wife however uses Nvidia GTX 1080 ti and earlier GTX 970, and both games worked perfectly for her too using Debian with both cards. My wife also played lots of portal both 1 and 2 with Nvidia cards.
In short those 2 games should work fine out of the box, with both Nvidia and Radeon. So maybe you have some hardware problem? Or something with your installation was screwed up somehow?