Not recommending software. As you mentioned old hard disks, it is better to copy the files or better dd them on a ssd. That way making index and finding duplicates will be faster cause you’ve to access files once and not care about fragmentation if you dd.
You say KDE hangs, but what component hangs actually? It it plasmashell (other apps work but panel is dead?)? Kwin (windows move/respond to input?)? KDE apps?
I would suggest you to install a distro with kde (fedora KDE edition or open SUSE, not neon) if you’re not confident with administration. Use something like Kinoite for accidental breakage protection, or if you want to keep /home as is, install fedora 42 inplace (the new installer).
Not only my experience but also that of many KDE devs say that fedora KDE is probably the best mainline KDE experience (ignoring niche distros or customized KDE).
Also, don’t use xorg session. Always log in to default wayland session unless you have incompatible usecase (in that case you know what you’re doing).
What’s the problem with it? These MIT programs already exists. Anyone can make proprietary version. Including in Ubuntu doesn’t change that.
Also your example is pointless. Canonical would rather make a proprietary pam module instead of a custom internal fork of sudo-rs.