Uninstall the gnome desktop package, reinstall the kde desktop package and that should pull the overlapping dependencies. Might need to do this from a virtual terminal, not in the desktop environment.

Or reinstall the OS.

Edit: there's also dnf swap command available for fedora, I'm not really familiar with it's behavior or how it acts when both DE are already installed, but maybe that could be a lead.

Edit 2: after doing reading, I'm confident you can just dnf remove @gnome-desktop. The .config files will not be impacted. Applications with overlapping KDE dependencies will belong to two groups, and the operation will keep the ones that include the KDE group. I still recommend a backup.

Have you thought about biting the bullet and just doing a full wipe and fresh OS install? I recently did this with a fresh, minimal Debian install, and it was so worth it.

I suppose Fedora works similar to Debian handling dependencies, thus uninstalling libgtk* should trigger removing all GNOME/GTK packages and apps. Removing a metapackage, like it's probably gnome-desktop, usually does almost nothing.

Edit: You can reinstall the GTK apps you like to use, e.g. Firefox or LibreOffice, later, as the user config files are not going to be deleted.

Edit 2: Maybe I've misunderstood: Do you want to keep the GNOME login session an desktop environment but use KDE apps like Kate instead of gedit?

A question related to this: is there a way to remove pre-installed apps on gnome? I have tried to uninstall them, but the system won’t let me.

Try to find the Fedora/yum equivalent to

apt-get purge gnome-desktop

apt-get autoremove

I think you already got a good answer but let me throw in another:

Fedora's dnf provides some good history and update reversion tools. You can use:

dnf history list

to get a list of all actions taken on the system since install. Use "dnf history info 5" to get info on the 5th transaction. (Get the transaction ID numbers from "dnf history list".)

Then to revert a change use either:

dnf history rollback or dnf history undo

Using undo reverses a single transaction, so if you have one where you did something like "dnf install tmux" and then ran undo on it then that would be equivalent to running "dnf remove tmux" in terms of what it does on your system.

Rollback does what you might think: it basically goes through all the updates between the most recent and the one specified and it reverses each of them, theoretically restoring the system to the state it was in at that time.

I say "theoretically" because this isn't a perfect system. For example, if you have an update where you removed some software that had some customizations done to it and then went through a rollback it'll put that software back but may be missing configurations you applied to it, so potentially it could cause some issues if those were important. This gets into a lot of complicated stuff and tbh it is a powerful but imperfect system. Something like Atomic gives you more of a guarantee that a rollback will work because the whole system state is defined by the installer, not just the packages.

There's one more note: Fedora removes old versions of packages from its repos so you'll need to add their historical archives repo to do certain things. I forget how to do that off the top of my head.

This may not be what you want exactly but it's a powerful tool that's good to be aware of.

See this for more info.

Which distro?