Qt Designer integration in CLion is nowhere near as smooth as in Qt Creator, but you can still make working with .ui files reasonably convenient.
In this episode, Jesper Pedersen shows how to configure an External Tool for Qt Designer that always opens the matching .ui file next to your current .cpp, and then bind it to the familiar Shift+F4 shortcut so you can jump from code into the form editor with a single keystroke – plus a quick bonus on re‑binding “Open tab in new window” to Ctrl+E,4 to better mimic Qt Creator’s window handling.