Cellular versions of Apple's sixth-generation iPad mini don't support mmWave, a faster 5G protocol that's predominately used in the United States, at all. As for the new iPhone 13, it still restricts mmWave 5G support to the US just like its predecessor, the iPhone 12 family.
mmWave 5G support: Non-existent on the new iPad mini, limited to US-only iPhone 13 models