6.4 broke progress bar on file transfers (already reported a bug), ~~slso~~ also the new interface file transfer is ugly, too busy and missing the part where it tells you how many GB of your file has been transferred. I hate it. Sometimes things don't have to change just for the sake of change. If it ain't broke don't fix it.

6.4 broke HDR for me lol

This update broke my plasmatheme and it has a weird gap on the top when tile window side by side, it also broke "kde rounded corner" desktop effect. PS: the new floating applets are nice, but hard to distinguish between it and app background when using any themes that isn't grey or white, they really need to implement border around the panel and applets.