The folder `dist/build/mv3-data` will cache data fetched from remote servers, so as to avoid fetching repeatedly from remote servers with repeated build commands. Use `make cleanassets` to remove all locally cached filter lists if you want to build with latest versions of filter lists.
The file `dist/build/mv3-data/log.txt` will contain information about what happened during the build process.
The entry in the `Makefile` which implement the build process is `tools/make-mv3.sh [platform]`.[1] This Bash script copy various files from uBlock Origin branch and MV3-specific branch into a single folder which will be the final extension package.
Notably, `tools/make-mv3.sh [platform]` calls a Nodejs script which purpose is to convert the filter lists into various rulesets to be used in a declarative way. The Nodejs version required is 17.5.0 or above.