Solved

I can't find my league

I suppose it's this one: https://igpmanager.com/app/p=league&id=261376&tab=info

To find leagues, teams, managers and, less so as there's really a lot and several with same name, drivers/staff there's a search button on the top right of the Home page of the game.

Also, if you plan to use the league publicly but not joining, a host not racing in the league is considered inactive by the game and any established manager can take over host of it at any time by hitting a button.

There's another league only search in League > See other leagues, you could try that. In game I'm not aware of any way to shortlist leagues. In browser you could bookmark the link, for the App perhaps put it in a note.