For now, I think I found the issue. The new shim is signed with both 2011 and 2023 keys and my pc only has the 2011 keys. For some reason my PC is rejecting the shim signed with both keys so I had to remove the 2023 signature. Maybe downgrading the shim to the previous one should also work.
Any Proxmox devs around here might benefit from this finding. If you read this, please reply.