On Earth, unlike what's often claimed, the largest current flying birds don't approach the size limit for flight with Earthly biology. Quetzalcoatlus might be getting close to the limit, though. A big one might be 250kg with 12m wingspan, and the flight performance of pterosaurs is still debated, but some scientists suggest it was too big for flight powered by aerobic respiration and thus could only sprint short distances (without updrafts or tailwinds to help).
Now, take what I could term "Flyers' World" because it's easier to take flight. 10atm, 0.5g (That seems to be about the lowest gravity that could maintain an Earth-like atmosphere -- I justify pushing to the limit because the denser atmosphere gives a stronger greenhouse effect, meaning a slightly lower upper-atmosphere temperature for the same surface temperature, and that's where atmospheric escape happens. But back to the main point...) But how much easier? Assume biology close to that of Earth vertebrates (birds, bats, pterosaurs). How big can the biggest fliers be?
Yes, I've seen Size cap for alien sky-whales on a high gravity dense atmosphere planet Not nearly enough information, and it's about buoyant animals anyway. More on target, I've seen Will my bird likely be able to fly in this atmosphere on this planet? but I need to go beyond just the thrust-weight-lift-drag relation. I'm asking... At what size will its muscles no longer generate enough force to flap its wings, or its wing bones break under the force of that flapping? What other things do I need to consider? I'm looking for consideration of multiple parameters, as I don't know which will be the limiter.
I recognize there won't be a published answer to this exact question, but I'm looking for calculations based on properties of Earth animals and their tissues.