I’ve worked with UE for a while and am happy when the joints come in working well enough. I’m surprised rigs successfully export at all. As far as I knew the rig would have to be added in UE after being imported. There are some plugins that add a rig in UE though I like to animate outside UE and import the animations. The only thing you might need a rig for is to have thing work in real time. Something like a tail swaying back and forth and colliding with meshes in real time would be something I would rig in UE.
I might have misread what you said. You saying you export the skeleton made with Rigify in Blender into UE then make a Modular Control Rig in UE. After adding the leg in UE the leg bends up?
When I try using a Rigify rig with UE5 Modular Rig it doesn’t even pop up with the shoulder circles after I apply the spline. It is still in beta. It is probably really picky about a few things. I’d find and download an example character in UE5 where everything is working with the Modular Rig then copy the bones, bone orientation, and names of the bones for the character. Next make sure it exports right from Blender after it gets in UE5. Next cross your fingers.
You mean Maya rig work well when imported to UE5 and Modular Rigs, or are you trying to export from UE5 to Blender?
Modular Rigs in UE5 didn’t seem all that great yet. When I tried it you can’t even hit undo without it breaking. I prefer animating in Blender over UE5. There are some cool things that can be done if you want a tail swinging in game without animating it first. That can be done without Modular Rigs though.
I have the same problem with simple handmade rig done in Blender. It may seem like only legs are broken, but in fact arms and shoulders are broken as well. Even on your screen, I can see your right shoulder control is misplaced. If you change arms to IK it behaves just as legs and vice versa, legs changed to FK work just fine. The problem is that at it’s core, Blender’s bone orientation system is not compatible with UE.
How I “fixed” the issue:
Use new UE5 tool “Edit Skeleton” in Skeletal Mesh asset, go to action “Edit”, pick every bone and under Details > Transform change it’s rotation to match Mannequin’s. It’s tedious, but I couldn’t find a better solution.
The Solution is to fix the transforms of your bones using the Skeletal mesh editing tools plugin via Edit> Plugins, and then searching for it and enabling it.
You can edit the skeletal mesh afterwards buy opening it, selecting the bones having issues, and then rotating the transforms to the correct orientation.
You want “Y”( Green) to be forward" and “X”( Red) to be up.
If you have animations tied to the skeletal mesh, this will affect them and you’ll need to re-apply weights using the same tool. Setting the correct orientation will fix the modular control rig though.