The A-shape minor barre right at the nut, the darkest of the flat-key minors.
Index finger barres five strings at the 1st fret (low E muted)
Load B♭ Minor (B♭m) onto an interactive fretboard, hear every note, and build it into a progression.
Play B♭m in the Studio →A B♭ Minor (B♭m) chord contains the notes A#, F, C#. It is built from the minor formula 1 - ♭3 - 5, with Bb as the root.
String tension is highest near the nut and the frets are at their widest, so the barring finger has to press further and hold more. The identical grip at the 6th fret is noticeably easier. If it buzzes, try it at the 6th, get the shape clean, then walk it back down one fret at a time.