Polestar 2 (Thunder/Slate)
So my initial assumption was that the .1 was the 1st release of that week, but I thought your suggestion made sense.P2111.1 Means 2021 week 11 day 1 (Monday). It was released on Monday.
However I got an update at Volvo earlier today, and the kernel was compiled Thu March 18, so three days later than week 11 day 1.
It also coincides with the day it was mentioned on their website, so I'm guessing either .1 doesn't really mean Monday, or I got a yet unannounced release (which is not very likely)