The 4K ultra fine specifically says in the docs about daisy chaining two together.
tb3 can definitely run two 4K displays from one port (I do it with a 2018 mini and a dual dp adapter) but that’s only gonna work if your gpu provides enough DisplayPort streams. I don’t see why a 2020 intel mbp13 wouldn’t run two 4K ultrafines daisy chained (the m1 Macs have limits on DisplayPort outputs)