Before none. I would normally aim to have some sort of warmup though so not going flatout from the start.
Afterwards, I tend to do my back, glutes and hamstrings. Pilates stuff mainly*. I find rolling with a stick or on a foam roller much more effective at promoting recovery. The stretches I’m doing are because I know I lack flexibility in these areas and they get tight while riding.
*pilates style movements may be of more help than stretching. Not the core strength stuff but the other parts which look at specific movements of joints throughout their range to loosen them up and improve blood/fluid movement.