So, this is kinda a tech support / bug report post...

The game is set to true fullscreen.

RX 480 / i5-6600k / 144Hz Monitor

When the FPS is set to be uncapped, it goes up to around 800 in menu, so clearly it's not that it's not capable of putting out that frame rate. However, both Vsync and Adaptive vysnc cap the fps to 60, which is not how they should be behaving - it should go to the highest multiple of the screen's refresh rate that it can exceed (in this case, 144). Normally I'd work around this by just setting it to unlimited, letting Freesync do its thing, and capping the frame rate through AMD settings, but Reassembly doesn't seem to respect those, and keeps putting out thousands of frames per second...

If this is just buggy that's fine, though I'd love if there was any advice to help.

Then you have a really good computer and don't need to put any concerns on that.

On the other hand, my computer is a potato and overloads 100% CPU usage with the game.

I mean, I definitely do. Rendering thousands of frames per second is a waste of power, unnecessarily straining on my card, and breaks Freesync. Furthermore, it's just not how vsync should work...