In some cases, the composer makes the video, and is sharing their own work.
In other cases, the transcribed part is not a composed part, and the composer who is listed (Lennon/McCartney) did not write or perform it (e.g. Ringo's drums).
In yet other cases, the composer was long dead before the recording was made, and the melody being transcribed is meaningfully different than the one they composed. Common in jazz.
"Composer" is a 19th century idea, enshrined in copyright law in the 1920's in order to protect the people who made sheet music for piano players to play in their parlor. Musical expression deserves attribution and protection, but let's not pretend the name on the liner notes is a Beethoven with a long quill creating a work of genius out of their solo effort.
https://www.thatgreatcomposer.com/blog/is-it-legal-to-transc...
https://law.stackexchange.com/questions/96352/dual-question-...
https://www.drumforum.org/threads/what-is-the-legal-basis-fo...
Inevitably the transcriber makes decisions in how to deviate from the reference recording, be it omission of instruments, microchanges in tempo and pitch or articulation. In theory a good transcription is an exact graphical representation of the abstract sonic intent of the artist.
Of course, if you are combining voices, changing chords, it approaches an arrangement which is a more creative endeavor.
Not under US Copyright Law, it isn’t. Transcribing is derivative, not transformative.
BTW, if it was transformative, it’d be fair use and legal, and you’d be contradicting yourself.