Desktop Linux’ marketshare is going to steadily increase, but as time progresses, so will the speed of that increase. Linux was at or below 1% for a really long time but within the last 5 years or so it jumped to ~5%. As this not only means more users, but also more attention and developers, this will of course snowball. The end of Win10 will also give a bump. And if the enshittification of Windows continues (it probably will) and if US-based companies are becoming a red flag for non-US-customers (will probably also happen) then it will snowball even faster.
Not sure there will be a big change there, because they are already powerful enough for most common tasks since several years now. And everyone owns at least one phone or tablet already. So I don’t think that number is going to rise significantly anymore. Those people who are OK with using a phone/tablet for everything probably already do so right now. Maybe if living conditions for the non-super-rich become worse and people look for more affordable computing devices. But even then, older devices which can run Linux desktops for example are already dirt-cheap. I just don’t think that the UI/UX of phones or tablets is on par with desktops or notebooks running a regular desktop OS when using a big screen. Those UIs are primarily made for touch and for smaller screens. Trying to do everything with just one UI paradigm just leads to Windows 8 ugliness.