There's an object lock feature which prevents objects in a certain bucket from being deleted before X amount of time has elapsed. This might be able to prevent

There's an object lock feature which prevents objects in a certain bucket from being deleted before X amount of time has elapsed. This might be able to prevent backups from being tampered with. If that doesn't work, there's a restic server which can act as an intermediary and which has an append-only mode which would prevent backups from being tampered with if your computer were compromised.