This is what worries me. I’ve used Time Machine for almost 20 years and it has provided seamless transitions to new MacBooks. But how do I know if it is currently borked?

I heard in the past that Time Machine backups would inevitably become corrupt because of a fundamental defect. Pretty vague, I realize, but I wouldn't have used it anyway; I rely on Carbon Copy Cloner to back up only what's important.

The problem was directory hard links. Fortunately that particular issue was resolved by replacing it with APFS snapshots. But the reputation damage is done; I don’t really trust Time Machine.

test your backups. disaster recovery gamedays shouldn't be optional. you can spin up macos vms on your mac (or in qemu on linux if you want, or in docker, or rent a mac cloud vm) and test the backup restore.