I tried to install CachyOS with KDE on my wife's new laptop (Lenovo Yoga) about 3 weeks ago. The version available was 2025-08-28 (still is, just checked), and it was crashing KDE all the time. Quick research told me that version had lots of KDE bugs that have been since fixed, yet no new release.
Maybe it's different on Nvidia (wife's laptop had AMD graphics), but I expect a very bumpy road ahead of him.
I absolute love KDE Plasma but I finally gave up for Mint Cinnamon LTS.
It has just been rock solid on any machine I have tried. KDE I was just always running into some kind of minor problem or something wouldn't work.
I have dolphin and konsole installed and open right now so once you get use to Cinnamon, it isn't really that much different but so rock solid with Mint.
Have you tried updating everything using "sudo pacman -Syu" ?
I just had to update my CachyOS install last night, as some software I wanted to install was just getting 404 responses from the repos. Turns out they don't keep round old packages? I dunno, but the update command above fixed it.
No, I didn't, after the third freeze and reboot I just thought "why am I wasting my time on this crap?", wiped it and installed regular Arch Linux instead. That one was stable out of the box.
Maybe it's different on Nvidia (wife's laptop had AMD graphics), but I expect a very bumpy road ahead of him.