This isn't true . You can go to lineage os home page and under wiki instructions you can use the copy partitions zip. It copies what's on current slot which would be A11 in your case. To the opposite slot. This is what it's for. Give it a go
Oh. I didn't realize that the script would clone active to inactive. I thought it was just A to B, but looking at the script, it does define active to inactive. That's my bad.