First of all: there is no BIOS for a processor. BIOS is for the mainboard.
There have been no official updates for the ASRock B450M Pro4 since 2022. However, ASRock offers beta versions (run stable). So that your motherboard gets some security-relevant updates.
The latest version is 10.31 [Beta] from 26.08.2024. You can find it here:
https://www.asrock.com/mb...