@fpotier First of all, you need to create your build environment. This is achieved by using lxc containers:
On this thread, later on @Gustl22 has posted some more advices.
The build script is located in GitHub itself, under:
E.g. to compile Seafile server v8.0.5:
$ wget https://raw.githubusercontent.com/haiwen/seafile-rpi/master/build3.sh
$ chmod u+x build3.sh
$ ./build3.sh -D -A -v 8.0.5 -h https://raw.githubusercontent.com/jobenvil/rpi-build-seafile/main/seahub_requirements_v8.0.5.txt
After you built the binaries, paste the link to your tar gzip files here or create a new thread announcing them and I will upload those to GitHub, exactly here: