These photos show two different individuals of Megachile(?) sp. in the same location: Garden in north-eastern Lower Saxony. Unfortunately, I don't remember the exact size, I think it was about 8-9 mm.
I add a photo of a female entering a clay-hole (same location). There's nothing to see but the orange pollen brush and the white hind margins of the tergites, but maybe it helps in combination with the other pictures.
best wishes, Jann