In NuestraRed for some equipments we are using OpenWRT version 19 with the LibreMESH packages, normally what we do for the Firmware is compile it based on the official OpenWRT branch and add the packages we need from LibreMESH and custom configurations for the network, in the documentation.
Soon I will publish in this link the things that must be taken into account to have the LibreMESH packages working in OpenWRT version 19 to create a mesh network. https://docutopia.tupale.co/Compilando-LibreMESH