Upgrading, like from Debian 12 to 13. It's too complex, and if you install anything out of the ordinary (which you have to if you want packages from this decade), things get even more complicated.
I've used the same Arch installation for 14 years and only had issues when we switched to from sysvinit to systemd in 2012 because I didn't read the news. Easily fixable though
Apt is one of the worst package managers I've used. Yum is also trash, dnf a bit better. But pacman is by far the best