I'm pretty sure a non-technical user can use Ubuntu or something, from start to finish, without ever touching a terminal.

To me, the main issue is that many preferred softwares are not offered on Linux because of its small market share. The market share doesn't grow because preferred softwares aren't there. It's a circular problem.

That issue is improving all the time though as new softwares tend to target Linux natively (ex. Discord, Zoom, Slack). Furthermore, the compatibility layers are getting better for non-native programs (ex. Steam deck).

I really don't see a universe where Linux stops taking over the world, including the desktop. Adobe and Excel probably can't hold Windows up forever.