Multi-cursors or multi-selection are one of those features you start loving once you first try if only they're implemented correctly, UX-wise. I think the first guys, who made these features really useful were the guys who developed SublimeText editor. Just look what it can do:
Just in case Sublime is available for Linux and I also heard the same features been supported by MS Visual Code studio, which is also available for Linux. But all that off course is not an open-source software.
Speaking of KDevelop and Kate editor. They're both built on a top of KTextEditor KDE component. There were number of attempts made in the past to introduce these kind of advanced multi-cursor and multi-selection features on a top to what it already had (multi-cursor via block selection - https://kate-editor.org/2013/09/09/multi-line-text-editing-in-kate/ - which is pretty limited in terms of what you can do):
Unfortunately none of them were eventually merged to a mainline.
So if you want to use one of these, you'll probably need to build it yourself.
But things has changed to a better just recently. From what I see in the recent news is that KDE dev team was advertising to support multi-cursors in KTextEditor starting from KDE Frameworks version 5.92 - https://kate-editor.org/post/2022/2022-03-10-ktexteditor-multicursor/
I guess it will take another while for major distros to update their KDE packages up to that version, so everyone could start enjoying multi-cursor and multi-selection in Kate. If you want to use it earlier you need either to build it yourself again, find a flatpak/appimage/snap package or just switch to KDE Neon :)
The world of Linux is tough one, yeah