Linux supporting all common end user applications and games, and working with all consumer hardware reliably, and having an intuitive and modern looking UI.
Also not having to wonder which distribution to install because MyAss_OS! works best for Steam but FuckNux works best with video editing software and you happen to need both.
I use Linux all the time, I have servers to host my websites and a NAS, and I install Debian on all of them and have no problem administering everything, but you have to be blind to not see how Linux is an extremely hostile environment for consumers.
I would never consider installing Linux on my personal desktop for those reasons. I honestly do not even know which distribution would be suitable, given that I do everything from programming, to gaming, video editing, browsing, basic stuff on Office, 3D modelling and printing, etc. from this computer. There's literally no way for Linux to support all of this, and even to get 50% of the way there would be a huge headache with emulation and following half outdated tutorials.
"Oh, you want to install <common software>? Sure, just add this totally not sketchy repository and run this command which will work only Debian Bookworm. Oh, you have another version? Then ignore what I said before and run this wget command on https://haxx.notavirus.net/sexy-girls.exe and run install.sh as root. Oh, it errored in the middle of the installation? Here's a link to the solution on a decade old forum post that is now a 404."