I’d think you’d have a very hard time to get reports other than anecdotal ones about this specific topic, so totally fine. As I have no AMD iGPU available to test, I have no idea how common that kind of problem is.

But sounds a lot like either the AMD Linux driver or the Steam Big Picture implementation for Linux does things wrong. I believe I explained it in other posts, that I would not expect it to directly impact performance, but any program that treats this like a dGPU and tries to manage memory on a low level will probably handle things very wrong when only tiny amounts of memory is allocated.

And while I have no deep knowledge of GPU APIs, which API is used should influence greatly, how likely it is for an application to bake in a way that only works for dGPUs or high amounts of UMA.