“You cannot merge a PR in the middle of the stack before the PRs below it are merged.”

Huh? Some stacks need to land all at once and need to be reviewed (and merged) from the top down. It’s not uncommon, in my org at least, to review an entire stack and merge 3 into 2 and then 2 into 1 and then 1 into main. If 2 merges before 3, you just rebase 3 onto 1.