Is it possible to specify a gitlab runner by name?

It's not possible. The runners can only be selected by tags and runners with an identical tag should be homogeneous in terms of software versions and hardware. The fist one that is ready to take your CI job will run it. So one should never need to select a specific runner, in a group that share a single tag.

Each job may known the runner executing it by looking at the environment variable CI_RUNNER_ID, but this is not usable for your purpose. Unless you force a job failure if the runner is not the "good" one, and retry it until it will be randomly taken by the runner you want. But of course this would be a weird solution.

No. The documentation is misleading. You can only use tags to limit what runner(s) your jobs run on.

The only other way you might have around this would be to register your own runner(s) for your project/group, giving them the tags you need. Though, I doubt that's an acceptable solution for obvious reasons.

Ultimately, your GitLab administrator will need to configure your runner(s) to have an additional tag by which you can uniquely identify the runner(s) if you want to be able to have your jobs use a specific runner out of your shared runner pool.