Windows is messing with that. A feature of modern UEFI boot, that OS-s can change boot order. This can be useful, after OS installation you don't have to manually change back boot order from the usb to the internal drive. The problem is usually windows like to reset this to itself...
Arch wiki has an article about this, try to set this options in your BIOS: https://wiki.archlinux.org/title/Unified_Extensible_Firmware_Interface#Windows_changes_boot_order
I guess with the bios update some settings were reset to default, that's why the behavior changed. Maybe reset your bios settings, and try to set up everything again from scratch, some old settings may be still active from the old firmware, etc.