I'm wondering if any of our usual techie folks have real-world experience or thoughts on this?

I don't have any recent practical experience of Windows anti-malware so my thoughts on it are purely theoretical. I think running two products that use the same privileged deep access the operating system is a bad idea. Hopefully each of those products is tested with Windows and their authors are aware of changes and planned changes in Windows. But I doubt if they are tested in combination with each other. Microsoft certainly advise against running defender and another AV product.

Which products have 'privieged deep access' and which use normal user-level file access (albeit with elevated 'root' permissions) you have to judge. Malwarebytes was just a file scanner when I last knew it 15 years ago.

For the same reason, I would think twice before installing any non-microsoft 'security' software because Microsoft does not, I assume, test 3rd party products with each update to Windows.

I went looking for expert opinion. Not from the product suppliers themselves, or from sites that have an interest in these products' existance - for example they take adverts (computer magazines as they would once have been). Brian Krebs for example. I've certainly read opinions that 'security' products - even the fact that Microsoft provides deep-level interfaces for them - actually decrease security. But I didn't find anything recent.

My wife has just bought a Win 8 laptop to replace her 10 yo Win 10 Thinkpad. Investigating how to restore her backups to it I discovered that Microsoft had deprecated File History Backup since 2017! Microsoft wants us to use, and pay extra for, OneDrive storage. I thought File History was the best feature in Win 10 and she's used it ever since. But I discover it still works in Win 11 if you can find it. (They did something similar to the previous Windows Backup.)

I'm not even sure that Defender still exists as a separate thing. 365 seems to offer something in this area but I'm not sure what. If the AV features (eg signatures, blacklists) are included in Windows that's fine but Microsoft are deliberately(?) unclear - they want to see cloud services.