This details projects using my RaspBerry Pi 4
To install gitlab on the raspberry, I used the official instructions at https://about.gitlab.com/install/
but with one addition: I had to override the locale settings, as I got an error message. Do export LC_ALL=C before the installation, and it worked for me. I used the setting sudo EXTERNAL_URL="http://192.168.0.XXX" apt-get install gitlab-ce where XXX is the ip adress of my pi.