Clients can't create symlinks on Samba share

Thanks to @grawity for hinting that my problem might be related to the protocol version. I found a solution that enable symlinks with SMB3 by adding the mfsymlinks option to the mount command like so:

sudo mount -t cifs //ip.add.re.ss/share_name /path/to/mount -o username=hostusername,vers=3.0,uid=clientusername,gid=clientgroupname,soft,rsize=8192,wsize=8192,mfsymlinks

I don't fully understand the difference between a normal symlink and the Minshall+French symlinks, but it appears to work for my case.

Sources:
https://www.systutorials.com/docs/linux/man/8-mount.cifs/
https://wiki.samba.org/index.php/UNIX_Extensions#Minshall.2BFrench_symlinks).

This way works for me:

sudo mount -t cifs -o user=user,pass=pass,vers=3.0,uid=987,gid=0,soft,rsize=8192,wsize=8192,mfsymlinks //10.10.10.10/git /var/opt/gitlab/git-data/repositories