Assuming this is an ATX or ITX PC, there’s likely a way to reset UEFI so you can disable fastboot and change your settings, or at least boot from a recovery USB.

There’s usually something like a button or 2 pins you can short on your motherboard to reset the settings. If your machine has dual BIOS, there will be a switch you can flip, though you’ll probably need to update the UEFI again once you do that.

In the worst case (and this should work on almost any device), remove the CMOS battery, let the device sit for a few minutes, then put that battery in. That should clear all settings, including fastboot, and allow you to do recovery stuff - just make sure you fix the time before going on the internet.