"Actually Ubuntu is not less usable than Windows 10."

For you and me maybe. But don't expect other people to have your standard of software choices etc.

The problem is Ubuntu, but that consumers have migrated from desktops/laptops to Phones. (Bad for Linux, and bad for society as it's much easier to be a non-passitive participant on a desktop/laptop.)

for most people app selection on ubuntu is big enough to never need anything more only professional/rare software sometimes has no support/suitable alternative

- Can I install my "favourite program" on Linux?

Well sure, it's supported on X, Y and Z!

- Oh but I'm on distro A.

Oh sorry, that's not supported. But here's a post by some guy on some forum who says he made it work by doing a bunch of complicated things no one understands.

We're talking about Ubuntu. Distro X is always Ubuntu. Y and Z are usually picked from Debian, Red Hat, Fedora and Arch

This is often no longer an issue thanks to Flatpak & Steam Proton built-in Windows emulation.

In addition, there's a significant subset of people who's only program they use is a web browser.

This is obviously quite doable with basically any distro.

Yes, while this has issues of its own (as long as the web services they are using are centralized and corporate controlled) I have observed the less technical users I have been helping with computer issues are totally happy as long as they sit in front of a computer with a web browser, where they can log in to their online accounts and get going.

Some might want a full mail client and possibly a printer configured and that's about it.