Refer to the Development page, use the v2020.4 tag for compiling the latest release: LibreMesh 2020.4 ExpansiveEmancipation.
The latest stable release is available as a precompiled binary only for devices within the ath79 target of OpenWrt. Look for your router model in our downloads website:
and double check the correct file to use using the information available on the OpenWrt wiki, see their Table of Hardware here.
For installation procedure read our Quick Starting Guide.