Digi-Key has a series of 12 videos explaining real-time operating systems, with FreeRTOS as the focus in example. Each video walks the watcher through a tutorial, then provides a challenge.

https://www.youtube.com/watch?v=F321087yYy4&list=PLEBQazB0HUyQ4hAPU1cJED6t3DU0h34bz&index=1&ab_channel=Digi-Key