I downloaded your .fbx and opened it in blender. There is nothing really wrong with your model from a technical standpoint. The topology on the shoulders is not ideal, but it shouldn’t bother mixamo. Mixamo doesn’t need particularly realistic anatomy or good topology. I rigged this absolute mess of a generative robot model years ago without any issues. It also doesn’t have fingers. It’s missing a head, and has an extra joint in its legs.
(with mixamo animations)
There’s also no overlapping vertices or flipped normals or anything in your model. I took the file you included and uploaded it straight to mixamo without any issues (besides the viewport stuff you can see there. I think thats an issue with safari or my adblocker)
I would say try restarting your computer, and test it in a different web browser, maybe allow mixamo through your adblocker if you have one.
Can’t give any advice for ActorCore or AccuRIG as I haven’t used either.
If all else fails, you can rig it easily with Rigify, which is prepackaged in blender but not enabled by default. It doesn’t include a library of motion tracked animations, but you get to practice animating by hand, lucky you!