Any 40gigabit Thunderbolt dock claiming dual 4K60 compatibility should support 4k120 on a single display. A higher end dock is the CalDigit:

https://www.amazon.com/gp/product/B09GK8LBWS

With people reporting some Chinese docks such as this properly supporting 4k120 on macs:

https://www.amazon.com/dp/B09WH18DST

Not cheap, by any means, but like you mentioned, it allows for much more than a couple of USB ports, and like I previously mentioned, it's not tied to a single display.