Who is the "manufacturer" in the eyes of EU?

[Ronen E]

2. The other company is labeled as a manufacturer and holds full responsibility. To allow them "being responsible", you need to provide them with complete technical documentation ("tech file").

There is no obligation (that I'm aware of) for a component supplier to provide the full TD / tech file (large parts of which might be confidential/proprietary). There is only an expectation to provide enough information to allow the legal manufacturer to compile their own TD. What exactly constitutes "enough" is negotiable commercially and depends on the particulars of the commercial and technical relationship.