@James Chan_110, Thanks for posting in Q&A. Based on my researching, I didn't find this feature in Intune now. You can feedback to see if we can have this in the future.
https://feedbackportal.microsoft.com/feedback/forum/ef1d6d38-fd1b-ec11-b6e7-0022481f8472
As a workaround, you can ask user to send email to the admin to request this. When the admin approve, they can add the user into the app deployment group.
Thanks for your understanding.
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