For me it's the fact that Ubuntu forcefully shove snap into my system when I want the normal deb install with apt. I'm sure snap has gone better over the years but this is something that I absolutely hate. When I want to use snap/flatpak, I can use snap/flatpak install, and when I say apt install it should be deb install as it's supposed to be as a Debian variant. Linux tools has always been known for doing exactly what is told, whereas what Ubuntu is recently doing is the opposite of it