There are lots of themes for KDE, but installing them can be a little messy. Unlike Gnome where it’s all handled through the dconf program, there’s some manual setup involved with KDE - config files, replacing icons in different directories, etc. For example, here’s a step-by-step guide to installing a beautiful KDE Nord theme, which turns into a bit of a PITA:

https://youtu.be/2GYT7BK41zk?si=INGkzL9sF5tkvm1q