On one computer, running 21H1 and latest patches and latest Edge, any support article at Microsoft, and only that, appears without the formatting. I am sure there is a setting causing this somewhere but I haven't found it. Here's what every support article at Microsoft looks like:
It is clear here that some .css files are not downloaded. If this only happens on certain websites, it's likely that it's blocked by one of the browser extensions, Adguard, or something else disables/blocks javascript. Disable one-by-one extensions, nb! sometimes is needed restart browser. In rare cases, some or all of the User Data file (s) are damaged. Try to make new User Data folder. It is difficult to guess anything more precisely from a distance, but the typical reasons are given above.