Exruder won't load fillament  

All I can think of:

Have you look in inspection door? See any filament going through? Maybe try loosen the idler a little bit?

Seems like something blocked or improper installing pinions on either X-axis or Extruder motor. I don't know. 

didn't help

I don't really get the idler's job, that's the long screw right? I loosened that and the fillament sensor screw, didn't help.

Through the inspection door I see the gears at first move when I'm supposed to push the fillament, but I don't see the thread going in anywhere. There there is another step where the gears try to turn but only vibrate, they are stuck I think.

I use enough force pushing in the fillament by the way, I know because I broke it when pushing too strongly.

Idler screw loosening

I had issues loading filament as well, and that was because it was missing the idler wheel. https://forum.prusa3d.com/forum/assembly-and-first-prints-troubleshooting/top-layer-under-extrusion-and-extruder-issues/#post-496423

Mine was the pre-assembled one so I presume you have all parts of the extruder. You shouldn't need that much force at all to have the gears catch the filament between it and the idler wheel. How loose is the idler screw? It should be rather loose: https://help.prusa3d.com/en/article/idler-screw-tension_177367/#mini

Posted by: @gald33

I don't really get the idler's job, that's the long screw right? I loosened that and the fillament sensor screw, didn't help.

Through the inspection door I see the gears at first move when I'm supposed to push the fillament, but I don't see the thread going in anywhere. There there is another step where the gears try to turn but only vibrate, they are stuck I think.

I use enough force pushing in the fillament by the way, I know because I broke it when pushing too strongly.

The idler is on the bottom of extruder. The long screw with spring on it. This is a tension - like putting pressure filament on the teeth of pinion. If it's too tight, the filament will have hard time going through. If it is too loose, filament will have difficult to move.

That's just one of possibility. 

Do you think you can disassemble the extruder? Maybe you can find what's wrong... It did happened to me with my MK3. I had trouble with getting filament feed through extruder. I had to take apart and assemble it and it fixed the problem. 

Arrow

Arrow points the way:

took it apart

I took the extruder apart and moved the gear that's on the motor shaft a little bit away from the motor so it would be flush we the filament spur. It was hard to do and I don't know if that's enough, but I got (with pushing with my hands) the filament through the extruder, however it stil barely moves and a long way from the nozzle.

Tighten screw

Have you checked that the tightening screw that keeps the smallest wheel on the motor shaft, is tight enough? It's a really small screw in the tread of the jagged wheel.

You shouldn't have to move anything around in there, since when you reassemble the extruder everything is flush fit anyway.

https://help.prusa3d.com/en/guide/how-to-access-and-clean-the-extruder-pulley-mini-mini_126457#126980

What Happends

What happens when you hand feed filament directly into the hotend?  Take the PTFE tubing out and hand load it.  

Posted by: @gald33

I took the extruder apart and moved the gear that's on the motor shaft a little bit away from the motor so it would be flush we the filament spur. It was hard to do and I don't know if that's enough, but I got (with pushing with my hands) the filament through the extruder, however it stil barely moves and a long way from the nozzle.

issue is found

The issue was that I attached the gear to the extruder motor upside down. Now it works. Thanks for your help.

Posted by: @gald33

The issue was that I attached the gear to the extruder motor upside down. Now it works. Thanks for your help.

That's good news! Happy to help you out! 👍 👍