What you linked is an add on GPU for items like a laptop. It is not a complete computer.
There are loads of options for mini PC, but (of course) once you start talking about the RTX level of GPU it's likely going to fall in territory that it's either a laptop form build inside a mini case, or things like M-ITX PC builds. There are some niche builds that a couple of manufacturers make but would be hard to specify a specific model, in that most of the time by the point you hear of or see a review they are already out of stock.
A lot of wind to say so little, I know, lol.
If you are looking for a true PC experience in limited space, look around at the M-ITX cases and things specified as HTPC cases, cubes, and things such as that. The Corsair One might be an option you would consider if you have the money....
But basically if you can find a case that you really like, that will actually FIT the planned GPU, IMO that is the hard part.
A couple of various suggestions based on super small size....Silverstone makes a couple of "HTPC" style cases that can fit a full size system. Lian Li makes some exceptional ITX cases. I use one now called a Rajintek Metis which is just about the smallest case I have used to fit a full size GPU inside. InWin makes a couple of interesting small cases. My suggestion would be to go to somewhere like Newegg and use their filters to see what is available. The single biggest issue will be the coolest and smallest cases rarely come with room for a GPU.