I use a modified UEFI, with the DXE driver designed to enable rebar on unsupported cards or, in my case, fix a card with bugged Rebar addressing. The UEFI has worked in windows all this time, and with or without the mod, linux would always resize the bar to 8 GB. From what I understand linux has always worked around this bug, and this bug is specific to the 5600 XT. Right now, the bar size is set to 1 GB in Bazzite but it should be 8, I'm unsure of how to fix this.
You can use Linux with 4G Decoding on, recent versions will automatically resize and allocate GPU BARs.
You can use Linux with 4G Decoding on, recent versions will automatically resize and allocate GPU BARs.