I think another issue with that build is they did not use thru-axles, at least on the rear.
so on top of new fork, groupset to go 1×12 you’ll be adding wheelset and new dropouts. Basically a whole new bike.
at that point, you’re better off building up from the beginning with what you want, or buying a better spec on the bike that needs less upgrading. The new SLX comes with 1×12 already and wheels that you don’t need to be in a rush to replace. SLX 12 speed really does not leave a lot that required upgrading. It’s a really good groupset.