Because the two terms and specs ('4K' and '120Hz', respectively) are becoming more and more intertwined, this is an increasingly common question. But the answer is a clear 'no' - for now. As it stands, it's still the minority of 4K TVs for PS5 and Xbox Series X that genuinely offer 120Hz capability, but much like all TV panel tech, it is beginning to become more prevalent and 'trickle down' through the tiers of televisions.
Thus, by default, not all 4K TVs have the refresh rate of 120Hz offered by HDMI 2.1 ports - you'll have to look out for these features specifically when you're browsing for TVs.