Ah. It’s never quite that simple….
68mm refers to the shell width. From memory, road is 68mm wide & mtb is 73mm wide.
So, you can swap to a Hollowtech II BB, but you would then have to go for a Shimano road crank; Sora, Tiagra, 105 etc. None of which appear to be single ring.
Or you might be able to run an mtb crank with spacers, but not sure how that would affect your chainline…it would push the chainring 2.5mm further out. I don’t have any experience with single rind stuff, so don’t know if that is an issue or not.
It’s never simple, is it? Maybe there’s a reason that all single ring road bikes (gravel/adventure/gnarmac…whatever they are called these days) seem to be fitted with SRAM….