This is good advice for organizations but if you are an individual GitHub user there is no way to have a pool of a few runners available for all of your repositories.

I don't know why but individual users have to create a single instance runner and mate it with exactly one of their repositories.

Converting from an individual user to a GitHub organization is not simple. The docs certainly make it look that way but I have yet to run into anybody that has done so without some form of catastrophic error that requires support to fix