T14s Gen4 AMD user here w/secureboot enabled. Just used fwupd to upgrade BIOS two days ago, because I didn't realize the BIOS boot-order lock was preventing it. Rebooted, changed setting, rebooted, upgraded firmware automatically, rebooted, changed setting back. Yes it took 30 minutes, but I don't expect I'll need to do it again.

While most of the hardware works, hibernate doesn't, which annoys me. Fingerprint scanner also only works randomly at login, Linux issue I assume. Machine was crashing once a week (logs suggest it was AMDGPU related), but not since the firmware update, so fingers crossed that's fixed. In retrospect I wish I got the L14, didn't realize I would need more RAM at the time.