I found this answer about Vulkan not supporting SM6 back then, but I think that my version is new enough, despite the cited warning that the layer is using version 1.3 instead of 1.4. I also changed to SM5 and deleted Binaries, Intermediate, Saved and DerivedDataCache and it still happened after building.
I know that the amdgpu driver is part of the Linux kernel, so the missing functions in libc (cited at the end) might indicate trouble with the driver, but I have no idea how to proceed.