Send from Gmail "plus" (person+something@gmail.com) address in Mail.app?
It's called an email alias.

https://support.apple.com/guide/mail/use-email-aliases-mlhlp1205/13.0/mac/10.15


  Create or change an alias
  
  
  In the Mail app on your Mac, choose Mail > Preferences, then click Accounts.
  Select an account, then click Account Information.
  Click the Email Address pop-up menu, choose Edit Email Addresses, then do one of the following:
  
  
  Add an alias: Click the Add button +, then enter a name and email address.
  
  
  
  Send an email from an alias
  
  
  In the Mail app on your Mac, move the pointer over the From field in a message you’re writing.
  Click the pop-up menu that appears, then choose an email alias.