Might as well contribute since this old zombie thread keeps resurfacing.
In lieu of instrument ground school, I watched
all of these PilotEdge IFR workshops to get a grasp on the system from the '10,000-foot view,' then used
these FlightInsight videos to better understand specific IFR topics, and used
Sheppard Air for written exam prep.
Later, I used ground instructor credentials to access the Sporty's CFI portal and watched all of their instrument ground school videos. I'm sure glad I didn't pay for that content, because the free stuff on YouTube was a lot more informative.
Sheppard is a grind and the user interface is trash, but it's hard to argue with the results. Follow their study strategy to a T and it's hard to score less than 95%.