Can an encrypted Android phone be unlocked with an USB drive some way? I want a fast way to login to the system without entering difficult credentials. If the usb key is not present there won't be the ability to decrypt the system ... Some 2-factor solution without NFC because the device doesn't have NFC.

Does somebody know how I could do this, because I can't find a way to do it?
No, this is not possible given how full-device encryption is currently implemented in Android. The bootloader needs your credentials to perform decryption well before anything like drivers for NFC or userland code is loaded.