I have exact same experience as you described. Don't like it at all. Below is my post where I explained the issue. To me it is a design problem that is only impacting MY21 Mild Hybrid, even though another 45e PHEV owner echoed same experience. Try driving it in Sport Standard mode and see if it improves (my assumption: in sport mode the brake regen doesn't engage).
https://www.bimmerpost.com/forums/sh...php?p=27554731
__________________
2021 X5, Excellence, M Sport, DHP, DAP, RSE, MW, Merino.