While 0W-20 seems thin, it is an oil viscosity that the vast majority of manufacturers have switched to over the past decade for emissions related reasons. With that being said, the latest version of the B58 (B58TU2) now uses 0W-12 oil, although that spec isn't in the Grenadier yet (I would imagine not for a few more years because it incorporates the 48v mild hybrid)...
More important than the weight number is that it meets BMW's oil certification, in the case of our engines, it is LL-17FE+; technically the various forms of B58s around the world can also use LL-04