The one they're getting people to switch their Mail accounts to - I'm using it now - is a bare-bones app that encompasses most of Mail's basic features, switches the look and feel a little (more irritating) and will automatically incorporate your Mail profile. The first email that appears in your Inbox each session is an ad. You actually do have a little control over it but it's just one more thing to manage and most people just ignore it.
Your need, if I understand it correctly, might also be met by using a single app with multiple profiles, one for each account. The freeware Thunderbird does support this. I use that on one of my older machines and it works just fine, and it works fine under Linux too. It's a little clumsy if you use features such as mass mailing from lists, but for single user work it's great. Those two, New Outlook and Thunderbird, are what I'm currently using on computers of several vintages (can't bring myself to toss a perfectly good 'puter just because it's old) and OS's, and will continue to do so until Microsoft pulls the plug on Win10 support in October '25, unless they change their current published plan. That's a different conversation, and that little time bomb is ticking. Hope this helps a little.
the Outlook that is free and replaces Mail
I have Outlook - that is part of O365, but also Mail. I use Mail for my personal stuff, and the Outlook that’s part of O365 for work.
MS is saying they’re replacing Mail with Outlook.