"Lock" brakes so that they are always active I have mechanical disc-brakes on my mountain bike. I am wondering whether it is possible to have the brakes activated without me pressing the levers.
I test-rode a trike that had a parking brake lever.  There was an extra button underneath the housing and when you pull the lever, it clicked in and holds brake lever locked down.
To release parking brake,  you squeeze the lever a bit more and the button pops out.
The brake is to help you load your cargo with the trike not rolling away.
https://www.huskybicycles.com/bicycle-brake-lever-wlock-v-type-left-hand.html looks like it.