@HerAdri this rather old writeup should help.
Troubleshooting libgit2
And this
Git Behind A Proxy Server - How to modify your Git commands for proxies - Guide - The freeCodeCamp Forum
git config --global http.proxy http://hemes:password@proxy05.ecp.elc:8080
git config --global https.proxy https://hemes:password@proxy05.ecp.elc:8080
I think you opnly have to set the http proxy
If this does not work we may have to set the HTTP_PROXY environment variable