Firstly, welcome.

I definitely support it, but I could actually enter the chords I think you are looking for.
I started a new song in the key of D Maj
I entered a C# and a G# chord
I transposed (Edit > Transpose > Transpose # of semitones) and also via the Key of Song setting.
The C# changed to a D# and the G# changed to an Bb, but I could then change the Bb to an A#.

Even with a song in the key of Db I could enter sharpened chords (see 2nd image)

I know you cannot enter Cb or Fb or B# or E# but you mentioned different chords than this.

Could you explain your steps further, also what version / build of BiaB are you running, and is this Windows or Mac?

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