It has always sat extremely unwell with me that the UAs were transmitting a message in Morse code. Why would aliens use Morse code, an ancient earth communication system.
THIS FOR ME! I have been asking that since people figured out the UAs were sending Morse.
Morse is a code (as opposed to a cypher). A code is a mapping from some
meaningful unit (word, sentence, phrase) into
something else (usually a shorter group of symbols). It would be extremely difficult to try to decipher a code if you did not know the language it was written in, similar to our problem with Egyptian until we found the
Rosetta Stone. You might figure out a pattern (short-short-long) but you really couldn't get more meaning out of that unless you had a codebook. Codes require a codebook.
If it was Thargoids, why would they use a human code which is unknown to most humans? Morse is archaic at best. More meaning could be had by a sequence of atomic numbers or frequencies, which would be universally known by a civilization capable of starflight. If you are trying to communicate with someone you don't share a language with, the first thing you'd transmit is a decode primer (see again Rosetta Stone) with, say, "iron = FE = 55.845 U = HELLO WORLD."
When we sent out the Voyager ships, we did exactly this; we also included music because those harmonic sequences are also universal (whether we like the sound/frequencies or not). Remember 'Close Encounters of the Third Kind'?
Also, we had contact with Thargoids before; we came to some kind of uneasy peace with them after awhile. Thus, they'd know human languages; why would they bother with Morse? If the UAs were merely transmitting an "i am here" signal, they wouldn't need anything complex; any repeating rhythmic signal would suffice (and be parsimonious regarding power and reach of signal).
I'm betting on the UAs/barnacles coming from a human source - maybe/probably the lost colony ships?