App Store still using my old email after changing it in Apple Account

What previous advice? What exactly have you checked or done?

Hard to offer any suggestions, if we don't know what you have already tried.

If its asking for an old email account, it either means the Apple ID using it is still logged in at Settings ➜ Apple ID ➜ Media & Purchases, or there are apps installed on the device that are still tied to that Apple ID, and trying to update. You would need to find and delete those apps to remove the Apple ID email entirely.

You either have a different account signed into Settings > Media & Purchases, or when you "changed" your address you didn't do it the correct way and instead created a brand new account.

If the first, go to that setting and make sure you are using the correct account.

If the second, it will be a lot more work getting that resolved. If you did create a new account you can try going back to the old account, but you will need another email address to use with it, or you can try to keep bth accounts going. This isn't going to be a two line solution so I won't bother with details until I know more about the situation.

Same here. I've had an Apple ID since... no clue, 2011 or so, always used it with my old email address. I changed the email address associated with my Apple account several months ago, on my 2023 Mac I've had no problems so far.

Now I'm on a brand new Mac mini with Sequoia, a computer delivered 2 days ago, that's never before known anything about my old email address. When I was asked to sign in to my Apple account during setup, I did so using the "new" email address, everything worked fine, iCloud connected, Apple Music, Apple TV+, everything knows me by my updated email address.

In Mac App Store, I'm signed in with the new email address. When I click my name in the lower left corner, then go to "Account Settings" in the upper right corner, it clearly mentions my new email address as my Apple account. "Media and Purchases" in System Settings shows the correct "new" email address.

I have Mac App Store set up so that it asks for my password for every purchase. For the first couple of purchases on this brand new Mac, when it displayed the account dialog, it always had my "new" email address in there, and everything worked fine.

But after a few purchases, it started always pre-emptively filling the account dialog with my old email address, that hasn't been associated with my Apple account for months now. For every purchase, I have to delete the incorrectly filled out old email address, and manually enter the current email address that I've been using with my Apple account for many months now.

Again, brand new Mac. Never used my old email address on this machine. Never been logged in to iCloud on this machine with my old email address before. Didn't log in with my old email address. Everywhere I checked, it's confirmed that I'm signed in with the "new" email address.

While I did purchase many apps while my Apple account was still associated with my "old" email address, on this new Mac there never were any apps installed while logged in with that "old" email address, since I never logged in using the "old" email address, only ever the "new" one.