MSFS ATC doesn’t know how to clear you to follow the constraints, but it will step you down instead, which is one reason I don’t use it. Pilot2ATC will give “descend via” (or “climb via”, but that’s rare, in fact I don’t ever think I’ve been given that instruction once) which will let you use VNAV properly. It’s also pretty good about giving you a TOD somewhere in the vicinity of what the NXi is suggesting, but unless you’re flying way up in the flight levels, which most NXi birds don’t do, it doesn’t matter all that much.