fritz@laptop:~/Documents/simbad3$ git commit -m 'Initial project versi
+on'
[master (root-commit) c5706b8] Initial project version
 2 files changed, 26 insertions(+)
 create mode 100755 1.simbad.pl
 create mode 100644 README.md
fritz@laptop:~/Documents/simbad3$ git push -uf origin main
error: src refspec main does not match any
error: failed to push some refs to 'git@gitlab.com/perlmonks/simbad3.g
+it'
fritz@laptop:~/Documents/simbad3$
[download]

From this you are trying to push a branch called "main" which doesn't exist. Your branch is called "master" - push that instead.

It is still unlikely to work because your remote URL looks wrong (it has no colon).