I have a task to delete over 11k old branches.
I decided to test it manually on the first one and it shows me the error:

I have reviewed similar topics here and I see only 2 things preventing the branch deletion:
1. Some active PullRequests are present
2. Branch restriction
I have double-checked both and there are no PRs and no Branch Restrictions.
It doesn't work for me either through the UI or through the git command:

Please, advise.