I mean, I understand that in US Taiwan is recognized as a country, in Italy Palestin is recognized as such too, but they are not officially sovereign countries and protest from mainland are to be expected because it's a very complicated international matter and of course China uses all the tools they have to support their position, just like the US.
Do you remember what happened when Trump recognized Jerusalem as Israel capital?
Conflicts over sovereignty on land are as old as the human race.
If only Catalonia was interesting enough for the US to send their army on the borders...
That's one big difference.
Anyway, de facto doesn't mean anything here.
Taiwan is officially not a country.
If you don't like the comparison to Catalonia, lookup Cyprus.