One of the emails that's been revealed as part of today's massive Xbox leak reveals that Phil Spencer was very keen on trying to acquire Nintendo back in 2020, and it seems Microsoft was supportive of it as well.
Spencer's email from August of that year mentions that Nintendo was "THE prime asset for us in Gaming" and suggests that Microsoft's Board of Directors would have been "fully supportive" if the opportunity arose:
As you can see above, the Xbox boss also mentioned that "getting Nintendo would be a career moment and "a good move for both companies", but admitted that trying to convince Nintendo "their future exists off their own hardware" was taking a long time.
In that very same email, it was also referenced how Xbox was coming quite close to acquiring Warner Bros. Games along with ZeniMax Media, but ultimately it was just the latter that ended up being bought by Microsoft.