Aargh!
https://insider.office.com/en-us/blog/redesigned-comments-in-word
https://developer.microsoft.com/en-us/office/blogs/word-comments-vba-deprecation/
https://insider.office.com/en-us/blog/modern-commenting-in-word
I hope I'm wrong, but I fear we have as much chance of turning back the tide as King Cnut (think I've got the spelling correct!) did, given this change has been in development for over 2 years.
If MS don't provide an option to choose classic or new comments, then I'm opting out of 365 subscription and reinstalling my Word 2013.
This registry hack involves Experiment... keys, and it will presumably only work as long as old comments are available in the distributed version you have, as I presume once the new comments move from Experiment... keys the old comments won't be available. And looking at the said registry keys, this will be rolled out across the whole office platform. I shall have to dig out my very old Excel as well.
Someone tell me I'm wrong, please.