About, "Would you mind elaborating on the use case for this, that is in what situations you need to create a branch from a tag that has no other marker?"
Hot-fixing branching from a tag is very common. It is odd to see this question.
For the moment, we are branching from git bash, but we are then not making use of custom flows in Jira.
This issue dates back to 2014. Amazing that it has not been implemented, being functionality that it already exists in git.
I just noticed that the issue is marked as closed. The latest Bitbucket cloud does not have it.
teo.morell180586480, this issue relates to Bitbucket Server. There is a separate issue tracker for Bitbucket Cloud at https://bitbucket.org/site/master/