Hi @Malof - I am not sure what exactly the Mixamo FBX file contains, but if it does contain the character’s skeleton in a bind pose and a deformable skinned mesh, you can extract an Actor from that.
Open your Asset Browser from the main Tools menu, and navigate to your FBX file in the Asset Browser. Highlight your FBX file, then Right+Click and select “Edit Settings” from the menu.
This will open the FBX Settings window, which will allow you to edit what you are extracting from the FBX file. If you do not have the CryAnimation Legacy gem enabled, you will only see three tabs in this window, “Meshes”, “Motions” and “Actors”. If the Asset Processor has already found animation in your Mixamo FBX file, it has probably already made a Motion out of that, and there will be Motion information in the Motion tab, as well as a Motion file noted underneath the FBX file in the Asset Browser.

In order to create the Actor manually, if the Asset Processor has not recognized that your file contains an Actor, you just need to add one using the Actors tab on the FBX Settings window. So go to the Actors tab, and click on the “Add another actor” button to add one.

Once you click on this, it should add the Actor to this tab. Check all the Actor settings are what you expect, and that it has the meshes you want by hitting the button at the far right of the “Select meshes” field.
So if there was a bind pose inside your Mixamo file, it should have found the root joint correctly, although you can also adjust which bone it uses as the root. Now when you hit the “Update” button on the lower right of the FBX Settings window, the Asset Processor will pop open a window, and process your FBX file to derive the Actor from it. Once it does that, you should then see the “Actor” file type appear below your FBX file in the Asset Browser as in the second image above.
One other thing you can do, if you don’t want the animation in your Actor file (i.e. you have an Actor file which is only the character in a bind pose with no animation) is to remove the Motions from being considered. This is optional, but if you want to clearly separate your Actor from your Motions, it may be helpful.
Just go to the Motions tab, and hit the “Add another motion” button to refresh the interface and add the little “X” buttons on the upper right of each motion. Then you can just click the little “X” button on each motion and remove all motions, so that ONLY the Actor is being derived from this file. This would only be the case if you didn’t want the motion - so if you want it, just leave it!
OPTIONALLY REMOVE ANY MOTIONS YOU DON’T WANT:

Now that you have an Actor from your FBX, you should be able to open it in the EMotion FX Animation Editor, as well as add it to an Actor component on your game level.
Hope this helps!