I would try opening Realm on browser (https://www.realmofthemadgod.com/). Enable Flash on the site if it is not enabled already:
Once it’s enabled and the game is running on browser, right click the game and go to
It should look like this:
If that box isn’t checked, then check it and close the pop-up and see if hardware acceleration works on Steam now.
However, this is just a hopeful stab in the dark to see if there is something that can be done to fix it. Someone else was facing the same problem, but their computer was fairly old and we determined it was most likely the graphics card was too out-of-date to support Flash hardware acceleration. We couldn’t fix it in the end.