So umm. B#. Apparently you can’t do this in notessimo. Unless my computer is screwed up or something…
B# = C…?
Tried it just now, sounds close enough for me 
It is the same…
B + halfstep = C
B# = C
Cb = B
It’s like the keys on the piano. There is no key between B and C.
Okay, thanks. But why wouldn’t you just use C then…
Music theory, when working on a score you want one version of each letter in a scale, for example in A# minor, you would have both B# and C# in the scale, and if you wrote the B# as a C you would need accidentals everywhere…
On a side note, you can do B# in Notessimo, it is displayed as a B but sounds like a B#.
It’s the same reason why G#=Ab, for the convenience of music theory, and it looks better.
If a “C” note came up in a song with had the notes B# and C#, the musician would know it’s sharp,
whereas in a song which had the notes C and C#, the musician would waste time looking to which C it was (sharp or no sharp).
But it changes back to B after you reload the song.
Lets also put it this way, a “Trill” that is noted by not the trill symbol but the actual notes going back and forth on C - C# - C - C# would need sharp symbols after every other C and natural symbols on the others. This is solved with B# - C# - B - C - B - C
Fb = E & B# = C, there are no black keys between the B & C & the E & F on the keyboard, unless the keyboard has 19 keys on 1 octave or more for calling a microtonal keyboard or something, the Derpsichord even has black keys between the E & F & between the B & C if you want a wolf 5th, you should need an expensive keyboard with more than 12 keys on 1 octave