Edit: as u/DarkSynopsis pointed out in the comments below, there is now a paragraph describing a steam release inside the official website. This is about as official as it can get.
Source: https://multiplayer.it/articoli/monster-hunter-rise-intervista-producer-ryozo-tsujimoto.html
Italian original:
Per finire, dobbiamo proprio chiedervelo: quanto sarà esclusivo Monster Hunter Rise per Switch?
Ryozo Tsujimoto: (ride) In effetti, siamo orgogliosi di annunciare che Monster Hunter Rise arriverà anche su PC all’inizio del 2022. Per adesso non possiamo dirvi altro, ma speriamo che il gioco vi piaccia in qualsiasi formato sceglierete di acquistarlo.
Translated:
In conclusion, we really have to ask you: How much exclusive will Monster Hunter Rise on Switch be?
Ryozo Tsujimoto: (laughing) About that, we’re proud to announce that Monster Hunter Rise will be coming to PC as well, at the beginning of 2022. We can’t really say much else now, but we hope you’ll like …