Is it possible to assign multiple Users to an issue?
It’s not possible, unfortunately.
One of the reasons is that assigning more than 1 user to an issue can often create a sense of confusion, like “who’s responsible for this task?” or “who’s the main contact person?”. With each team member taking ownership of their tasks, more work can be accomplished.
You can notify more than 1 user though, to get their attention on the issue.
In some cases:
If you have a large task or goal for multiple users to handle, consider breaking it down into subtasks and assign them respectively. You can refer here on subtasking.
Or if it’s multiple users working separately on the same tasks, you can duplicate the existing issue and then assign them.