Edit: It really was an issue with my mouse, I put it to pasture.
Constantly when I try drag & drop on Dolphin & Firefox, the dragging stops mid-way before I stop holding left click, it’s a showstopper for me using KDE. I found others have this issue as well but is there anything I can about it? I’m using Wayland, NixOS, and a Logitech G604 mouse.
I help old folks with tech stuff and have seen this a few times, first step would definitely be trying another mouse. If you’re particularly attached to this one, putting a new switch under the clicker is a little annoying but very doable