The bike is rated for a 45x700 tire, 50c fits but it’s tight. AFAIK the checkpoint is not rated for 650B at all, however if you google, people have done it, but I can’t comment on clearance. I wouldn’t recommend 50c on the checkpoint unless you really know what you’re doing (a lot of people in this thread seem to not) - clear vinyl frame protection, dropouts adjusted correctly, wheels that aren’t trash, etc…
EDIT: maybe the newest version of the checkpoint is rated for 650? I thought at the time (2020) it wasn’t but that must have changed.
On a side note, the enve isn’t the first bike that can fit tires that size and the new specialized tire isn’t the first 47c tire so I’m not sure why people are acting like gravel racers haven’t had the opportunity to experiment with wider tires yet.
Secondarily, if you look at BRR and/or actually have first hand experience; gravel tires aren’t actually faster than XC tires unless we’re talking about basically slicks.