Thunderbolt & Graphics Adapters

Ok, so my knowledge on PC hardware and how it functions has clearly waned over the years, so I need some guidance.

If you have a laptop with, let's say, integrated and an Nvidia GPU in it, and you have DisplayPort/HDMI/etc external ports ... it use to be that with early version of HDMI and DisplayPort those connections could serve a single monitor each. Now I see people using Thunderbolt 3 docks and serving out multiple monitors off of a single DisplayPort connection. BUT, I always assumed those had a cheap GPU build in so all the rendering was done inside the dock. The other day, someone said "no, with some of the laptops, you could have 2 external 4k monitors at 120hz off the Thunderbolt 3 dock so you only need to connect 1 cable to the laptop and it all renders off the internal GPU of the laptop so you can still play games and do it all over the one cable to the dock".

Is that true?? Would that work on a Razer Blade 15 Studio?

I'm trying to make this thing easier to move around as I game with my kids in one room, but I use it as my work PC in my office too. If I could have this thing down to 2 plugs (power + dock), and still be able to connect my two 4k monitors running at high refresh rate when it's at my desk, that would be amazing.

Thanks for any clarity you can offer!