Might also be worth getting the back half of the handbrake cable out of the car and soaking it in crc/inox and manually moving it back and forth.
We had an issue with mine not wanting to apply a few years back and it had massive amounts of rubbish inside the sheath protecting the cable. After a few hours and getting a bunch of dirt out it worked a lot better afterwards.
This was very helpful: https://www.supercheapauto.com.au/p/bike-service-bs-cable-wire-lubrication-tool/SPO1893401.html