Having the same issue. I’ve put in a support ticket, but haven’t gotten a response yet.

Most likely there was a firmware update. If using refind for dual booting do the following. Boot into the bios (Volume Up + Power Button) choose boot from file, find a folder named efi, you may have to check serveral locations, and boot steamcl.efi. Once back in steam switch to desktop open refind create a new config and install config. That should fix it.