According to AMD for Zen2 Rome CPU microcode 0x830107b is recommended as per https://www.amd.com/en/resources/product-security/bulletin/amd-sb-7008.html
This is contained within amd64-microcode_3.20240116.2+nmu1_amd64.deb in the unstable/testing repos. https://tracker.debian.org/pkg/amd64-microcode