1080p 144Hz is the way to go, I reckon. You wouldn’t need 240Hz unless you’re in competitive gamer territory. What budget have you got for the monitor and what are you system uses? Gaming, photo editing etc?
If you're talking about an external monitor to run off the laptop, I'd suggest there's not much point going for more than 1080p 144Hz (either in resolution or refresh rate) as it's unlikely you'll go beyond that with the 3060 mobile in most games.