Bug Rigging for Unity, blender rigging cause mirrored bones?

There is a known issue where models on blender have mirrored bones in Unity.
Is there a way to solve it?
What are the limitations of Unity that don't allow it to use all blender rigging? How to work around those Unity limitations?
If I am to to pay a 3D artist to make a rig that is Unity compatible, what should I ask him to do?
Or is there a way to easily fix this known issue?

 

A control rig and game ready rig two different things.
A game ready rig cannot have bendy bones and should not use squash-strech effect.
A good resource for blender to unity export. https://polynook.com/learn/how-to-export-models-from-blender-to-unity
Cgdive's video series about contex:

 

What Blender rig are you using?

 

What does that mean? How can I find out? It's not SMPL I think

 

Human, meta-rig or Rigify variant? First the type you choose under Armature and if you then generate a rig or not. Maybe you've solved it already. I'm actually doing a tutorial in this subject but it's not done yet.