HarrietTheSpy
On May 19, I posted a temporary solution using a short macro and instructions on how to install it. It should be pretty easy to follow and does not require registry hacks or saving documents as macro-enabled. The solution has been working great for me, with just the slight inconvenience of having to save the document immediately after activating the macro.
https://techcommunity.microsoft.com/t5/microsoft-365-blog/introducing-modern-comments-in-microsoft-word/bc-p/2368481/highlight/true#M1841
I haven't seen much response to my solution, either positive or negative. I completely agree though with the comments against this new comment system, and Microsoft really needs to return this functionality without having to resort to registry hacks or macros. In the meantime, however, you could try this safe and relatively easy solution. If the instructions are confusing, let me know and I'll try to make them clearer.