You can try freezing the leaves in liquid nitrogen and use a mortar and pestle to crush the leaves. What does the electric blender do to destroy the phytochemicals?

use lyophilizer if available

Check https://www.amazon.in/Urban-Platter-Calcutta-Natural-Freeze-Dried/dp/B075VQWTG7

Also check https://masterchefmom.blogspot.com/2019/10/paan-spice-vethalai-podi-betel-leaves.html

Kindly check on this paper.

https://www.ijstr.org/final-print/june2019/The-Physical-Properties-And-Phytochemical-Exploration-Of-Bioinsecticide-Granules-Mixed-Betel-Leaf-Extract-piper-Betle-And-Srikaya-Seed-Extract-annonasquamosa.pdf

@Ayad Palani I have no such facility

@Chinaza Godswill All of these aren't quite useful because either they will destroy phytochemical or have processed compounds

@Kiprotich Kiptum Article didn't mention best way to dry leaves.