I am not entirely sure if this is a cachyos issue or a kde plasma issue but something I run into often, especially since the increase in ssd prices, is the need to transfer large amounts of data and subsequently check the quality of the data transferred from ssds to a hard drive. But thus far I consistently find that everything tends to freeze (especially dolphin and meld) during this scenario. And yes copying that much data over would work better through terminal, but often I need to determine the differences between similar directories and copy over only those differences. This tends to cause issues sort of regardless of how I do it - mind you the size of the files are often either hundreds of GBs or TBs in size (research related). And once any sort of file explorer tool inevitably freezes up, I pretty much have to hard shut off the computer and then restart again after turning it back on to get back into the system. It’s been a pain point thus far as it happens consistently when I need to free up space. Even through the command line I find things can freeze up when checking differences between files, and I’m curious if this is an issue related to how cachyos deals specifically with data from a hard drive and related slower transfer speeds.
This is what rsync is made for.
What you are describing usually only happens on lower end machines. It would help if you provided the output of inxi -F from you terminal. As for doing transfers / backups I use FreeFileSync.