In KBBvKQ it can take up to 142 ply, so 71 moves, to reach mate or a winning capture:Norm Pollock wrote:The 2 games that required more than 50 moves to checkmate had identical pieces but with colors reversed: KQkbb and KBBkq. Depending on the placement of the pieces, the checkmate would take about 75 moves (based on Ferdinand's previous post, if I understand it correctly).
[D]8/1q6/8/8/2B5/8/3K4/k5B1 w
https://syzygy-tables.info/?fen=8/1q6/8 ... _w_-_-_0_1
This position also happens to be one of the longest mates (81 moves).