Just to let you know the old mail app still receives mail, at least mine is on 5th Jan, but that dreaded "new" Outlook is still downloading itself and installing over the mail app.
I've tried the click Properties,/Security/Advanced/Disable inheritance as Mikkel suggests but that didn't work either, if there is a solution one doesn't seem to be obvious.
Still I'm having to uninstall "new" Outlook every time I want to use Mail, when will Microsoft get the message (no pun intended) people just don't want "new" Outlook.
I've also tried a few other mail apps and they just don't suit my needs, I liked the old mail app, I've been using it for years, without issues... it worked perfectly, no waiting for it to load, (like Outlook) no adverts, (like Outlook) it just worked, why oh why, couldn't Microsoft just leave things alone 😣