Where did You got such data from? I have a new Chromium Edge installed on several computers, and the old one is missing nowhere. They are completely independent of each other and even both can be used in parallel (simultaneously), ie at the same time. PS. The only thing that disappears is the icon on the desktop. Of course, if it was there before. And the reason is very simple - a new one makes an icon with the same name.
Kaljukass is correct, old Edge is never actually removed just "hidden" when the new Edge is installed, you can uninstall the new and then old Edge reappears, can't say it's "removed" if that's the case.
maybe is hidden because some UWP apps still depend of it ? so probably in the future Microsoft will remove it completely from the OS, and I guess if you remove it manually it could broken some things.
I can't download edge stable for windows 10. The site not let me. Not with edge classic, firefox or IE11. I have windows 10 19H2. So I'll stay with edge classic. Its favorites is better than in edge stable. I'll try in 20H1.
FYI, you can completely rip Edge classic out (IE 11 as well) and integrate Chromium Edge into a fresh image and install without a hitch. I have not had any issues at all doing this to 1903/9 or 2004.
Yes you can use it anytime you want. It is on its place and fully usable. It even exists in 19041,264. The only thing is that he now has a new name - Microsoft Edge Legacy. What's going on with it, don't know. So, use as much as You want, these are two completely independent web browsers and still exist perfectly side-by-side.