Can't update any firmware, I think RT-AC56U router was hacked

I have the RT-AC56U router for some years, I used it on and off, with even 1 year sitting connected but unused.
I remember I seen it 2-3 times showing some Korean or another Asian language when accessing the web interface.

Now when I searched about it, I found some references to hacked routers running similar firmware.

I can only access web interface, it says current firmware is 3.0.0.4.380_7266-g6439257

- if I check for a new firmware by web interface it says that none was found....

Can't update any firmware, I think RT-AC56U router was hacked