Also, if this were for a company I'd suggest to test the backup at least once during the object lock duration: e.g. if the object lock is set to 30 days, you have to test them at least once (e.g.: day 15).

That's because a targeted attack with a ransomware could gain access to your servers and wait 30 days while silently encrypting your backups until the 30th day, when the attackers could just complete the attack encrypting the rest of the files and showing the message.

So my recommendation for extremely critical data would be: 1) Test whole data thoroughly at least once during the object lock period. 2) Setup an automatic task that retrieves X random data every day (or the longest period of time you can afford to lose it) and perform checks with checksums or other methods. If something is corrupt and/or encrypted you will realize before it is too late.