You are on the latest release branch of the OPL. It is recommended that you just leave it as it is. Furthermore, you should upgrade with the "OPL-update" script. Not by running "git pull". The script will check for new releases for you and take care of fetching it.
However, if you are looking for something that is not in the latest release, the you need to checkout the main branch. Run "git checkout main" for this. Then run "git pull". (Note adding "origin" to that command is not needed and usually not even a desirable thing to do.)
You cannot run "git pull" when the release checked out because that is not an actual branch. The release is a tag.