Create a SubTask for a different Project -
Recently one from our user base asked for the above - We can link but why we cannot create a subtask for other projects from the current project?
It will be very useful to add that feature .
The subtasks must be in the same project under their parent tasks. If you want to create a task under another project, that's named Linked Issue.
So, you can create a subtask under a project A issue and link it to another task under project B which will probably be the best solution for your need.