There's a sub-reddit dedicated to online racing series that usually has a couple of Forza series going at a time. The LMP1 + GTE series just ended, a NASCAR series is going and an IndyCar series is about to start up. They do yellow flags for multi-car crashes, formal pace and caution laps w/pits closed until the field is caught up, and long races.

The sub-reddit:

The announcement thread for the IndyCar series: