That is a somewhat simplified definition of temperature. While there's a parallel discussion on the same topic at [0], the term you're looking for is Planck temperature [1]. There is no "upper cap" on temperature per se, but we also don't have any models for describing what would happen beyond that point. See [2] for more discussion.
[0] https://news.ycombinator.com/item?id=29963147
[1] https://en.wikipedia.org/wiki/Planck_units#Planck_temperatur...
[2] https://physics.stackexchange.com/q/420670/43412