I'm using a batch action that does some 'heavy lifting' with the selected rows. Therefore, after choosing the action, the page freezes for some time until it returns with Flash message.
Is there a way to customize the behavior (or an elegant workaround) to give feedback to the users on the progress of the action, while it's happening?
I could not find an answer to this on the documentation.
The short answer is no. You don't have a Flask-Admin way to do it.
If it is a long running task, you can handle it in background, using celery, rq or any other queue technology. This way, you return faster, but your task is still running. Just you can evaluate if it works for you.
If this solution does not fit your problem, you always can extend Flask-Admin to do anything the way you want.
I have some "actions" where I start the task in background and another page do polling to check if it is finished, but you use Flask-Admin just as a framework, it's not built-in.