Is it reasonable to consider that an encryption scheme must be invertible?
Am I correct in assuming that it is not wrong to impose the condition that a transformation must at least be invertible in order to be considered encryption?


Yes, strictly speaking: Encryption is the process of turning a plaintext message into a ciphertext (encryption) which then can later be turned back into the original plaintext (decryption).



If I am correct: Could I be pointed out to some reputable bibliographic source to use to strengthen my case?


Gary Kessler has published An Overview of Cryptography.
In chapter 3 &quot;Types of cryptographic algorithms&quot; you can see that there is a distinction drawn between encryption and hash functions.



If I am incorrect: Is it because cryptographic hashes are considered encryption schemes or because there truly are non-invertible cryptographic schemes? If so, how do they meaningfully differ from hashes?


Encryption, decryption and cryptographic hashes all belong together in the realm of cryptography but they can definitely not be used interchangable (see this earlier answer from a different question). Some differences include:
Reversability
Encryption schemes can usually be transformed back into their original form, i.e. a once encrypted plaintext message can usually be decrypted back into the original plaintext. Hashes, on the otherhand, are created in a manner that the input undergoes a loss of information, ultimately making it irreversible.
You can always create a hash from a given input but it's not possible to be sure what the original message once was if you're only given the hash (see pigeonhole principle).
Keys
Encryption schemes always use keys. Hashes do not require keys.
Length
A long plaintext message results in a long encrypted ciphertext &amp; a short plaintext message results in a short encrypted ciphertext.
Hashes will always have a predefined length, no matter the input.