I have a very cool Core 2 Duo laptop here that runs Linux Mint.
And it is pretty aweful. Would love to put Fedora Kinoite (Atomic KDE) on there, manual upgrades on shutdown, minimal set of apps.
But I dont know how well Plasma works on such old hardware. It is pretty bloated and messy sometimes, Dolphin and plasmashell are my biggest worries (the whole panel and widget stuff is sooo complex).
Has anyone tried Plasma?
An alternative would be LXQt with KWin once 6.1 comes out and it has full Wayland support.
I’ve used KDE on a Thinkpad T60, it’s about 17 years old, has 3GB of RAM, and a Core Duo. It ran surprisingly well. Replacing the HDD with a SSD can also make a noticeable difference, so you should consider that if you haven’t already. I also turned off a lot of the animations and effects for better performance.