draw polygone on the map

For inspiration, I have this example to extend the fionality of Phprunner maps, which I think you have the solution you are looking for.

https://fhumanes.com/blog/guias-desarrollo/guia-6-phprunner-indicar-direccion-a-traves-de-una-mapa/

Specifically, there are examples of https://leafletjs.com/ that do what you understand.

Regards,
fernando