I did an upgrade from 5.27 to 6.01 or whatever the latest is, and I had to go through themes and setting files and remove a lot of the old plasma 5 files. It is kind of a pain. I recommend doing a complete reinstall. I am sure some settings file from kde 5 is messing with your configuration. It is a pain, but probably the easiest in the long run.
It is not only BG3, it also happens in Skyrim SE, Fallout 4, nothing but Vulkan errors. I turn off Vulkan in Lutris and they run.
Some say the kernel is the issue, but I have tried a few different ones and same issue. I am at a loss. I am running Arch, AMD GPU.