What was the key length of the Enigma?
Enigma works with the idea of one time pad, it's a machine that automates key generation. In the one time pad, we have to generate a random key with the same length as plaintext but in Engima we make few setups, and the machine creates a that random key.
Here is the enigma procedure

A day key has the form


Plugboard setting: A/L–P/R–T/D–B/W–K/F–O/Y
Scrambler arrangement: 2-3-1
Scrambler starting position: Q-C-W


Sender and receiver set up the machine the same way for each message
Use of message key: a new scrambler starting
position, e.g., PGH


first, encrypt and send the message key, then set the
machine to the new position and encrypt the message
initially, the message key is encrypted twice