Most people use their computer solely for browsing the web and looking at images/videos, which linux is completely capable of. Next most used thing is office suites and printing - as long as you dont need to use right-to-left languages, the office suites are completely sufficient. Printers are dependent on the manufacturer, but most work, some with even less problems than on windows.

Now when we jump to the more niche areas, it depends on the area and your needs. Programming is obviously flawless on linux. Photoshoping images should be good enough for hobbyists, but not for some proffesionals. Video editing is really good for all levels, except fpr adobe products (davinchi and KDEnlive for example). Gaming works pretty well, and is improving over time. Other niche fields have linux support/alternatives, or their products may work through wine/proton.

At the end of the day, you can do basically anything on linux, not necessarily with the exact same tools as on windows.