USB-C and Thunderbolt 3 both utilize the same reversible port, leading to a lot of confusion surrounding the terms. While a USB-C port and a Thunderbolt 3 port look the same, Thunderbolt 3 has some extra hardware compared to the more widely-adopted USB-C. Remember, all your USB-C accessories and cables will work with a Thunderbolt 3 port. All Thunderbolt 3 ports are also USB-C ports. However, the same cannot be said for the other way around; not all USB-C ports are also Thunderbolt 3 ports.
Basically, it all comes down to data transfer speeds. Thunderbolt 3 can achieve data transfer speeds of up to 40Gbps, whereas standard USB-C can only reach up to 20Gbps, but typically gets lower than that.
Another advantage that Thunderbolt 3 has over USB-C is daisy-chaining. You can connect up to six peripherals to a single host Thunderbolt 3 port by chaining them together serially. This becomes super important if you want to chain together multiple monitors to set up a dual-display.
Most newer Macs have at least one Thunderbolt 3 port, if not more, so if you get a Thunderbolt 3 compatible monitor (which most of the options above have), you're going to be able to take advantage of more functionality and faster transfer speeds.