The timestamps being in the future due to a bug which has been fixed in 6.1. The bug is that restore assumes it can use the destination cluster to do version->timestamp conversion, which doesn’t work if you are restoring into a different cluster than the source of the backup.
That specific version mismatch actually should not cause a problem. 6.0.18 should be able to read backups created from (I think) 5.1 and later.
If you can reproduce the error, try adding --log to get a trace file, it may provide more detail.