You can probably use everything here in your other issue, which I guess got solved before debugging.
The error looks like TestHandler which is probably after the backup itself while Verifying backend files.
I’m hoping your bad files aren’t from the dates when OneDrive was internally corrupting uploaded files.
Microsoft fixed that in April 2022. Verification samples its backend files somewhat randomly, by design.
Once you get the failing files and their dates, that gives more to go on. You can also manually test files.