Deore FC-M615 single 64 BCD chainring
You need an offset chainring for this to work well. Otherwise the front chainline will wind up too far in, and when you're riding it with the small cog the chain angle will be extreme and likely problematic, i.e. as though you were crosschaining a double. There's a Wolf Tooth 28t x 64bcd ring that does this. (I'm assuming your frame is either 135 or 142x12; if it's Boost there's not a way for this to work reasonably.)

Presuming you're suggesting using the small ring off a double FC-M8000, that won't work because it's just a normal ring for derailleur use. In addition to not being offset and thereby putting the chainline too far in, it will want to cause rather than prevent derailment in the smaller back cogs when used without an FD in the way. There is zero reason to not use a proper NW ring.

Exactly how bad the results are if you go with a chainline that's too far in also depends on chainstay length and frame alignment.