Um, well, without better info I can only make wild guesses. One thing that could be happening is that if you’re working with what appear to be flat 2d meshes without any thickness with Dynamesh mode active, you could be inadvertently triggering the dynamesh by ctrl dragging a mask marquee in empty canvas. Dynamesh doesn’t work well with meshes that dont have any thickness, and will produce results like this.
Otherwise, I’m afraid we’ll need better info than that. Please post an uncropped screenshot of the active tool both before and after the behavior happens, and work a bit more mindfully so you can tell us exactly what you did when the behavior occurred.
This is the right click pop-up. It brings up a lot of useful quick access features wherever you’re working. You can disable it by going to Preferences > Interface > Navigation, and enabling both Right Click Navigation, and disabling the Right Click Popup. You must do both.
Be sure to store your config (Preferences > Config > Store Config) when making changes to the preferences if you want them to persist at startup.