Hi @Huayuan_Zhou, and welcome to the Forum!
Project filters do not include subtasks, so you will not be able to filter out subtasks based on custom fields or tags. This topic has been raised by other users, so you can vote on it here.
For the subtasks to be included in the filtering, you need to add them to the project. The filters work on a project level, and subtasks that are part of a task but not the project, will be excluded.
There is a popular thread in the forum requesting this functionality: Allow to automatically add subtasks to project In case you haven’t yet, I would recommend you to upvote it!
Perhaps creating 3 projects could solve your problem:
- Master project - to store work from both teams
- Project for team 1 - with tasks visible for team 1 only
- Project for team 2 - with tasks visible for team 2 only
That would make managing access much more streamlined. Alternatively, you could use a portfolio to manage projects of team 1 and 2 instead of a 3rd project.
I know these are not ideal solutions, but perhaps something will work as a workaround for your use case.