I updated to 18.0.1 and I also still don’t get any notification sound from the Mail app (Gmail account, uses fetch). I read in another forum that someone who has an Outlook account (uses push) updated to 18.0.1 and is now getting notification sounds with the Mail app. I wonder if this is a fetch/push issue. Disappointed because I was really hoping that this update would address this ongoing problem but it didn’t for me.
Apple technical support assigned me a case number and told me that the only solution to fix not getting a mail sound notification is to completely erase my phone and set it back up from scratch (not from a backup)… to fix a mail sound from one of their apps? There must be an easier solution but additional calls to Apple say that this is the only solution.