That scale finder view is kind of a misleading, if you are displaying notes instead of scale degrees. When displaying notes the tool shows the enharmonic notes always as sharps #. A mark x (Fx) is meaning a double sharp F##, which is enharmonically the same as G.
I suggest to learn the scales as scale degrees and fingering patterns, not memorize the absolute notes on each scale.
The key of Bb major is typically noted with a key signature of two flats. The flatted notes are Bb and Eb.
This way the notes of Bb major are
Bb - C - D - Eb - F - G - A (-Bb)
The scale finder tool present the enharmonic sharp values of the same pitches
A# - B# - Cx - D# - E# - Fx - Gx
This makes sense, why the key signature is 2 flats, instead of sharps