Does receiving grants make me a manufacturer?

No. Receiving grants does not make you a manufacturer under the CRA.

Grants provide financial support for the development of open source projects, but they are not a commercial transaction where the recipient is monetising a product that the grantor is purchasing. The CRA explicitly states that "the mere circumstances under which the product with digital elements has been developed, or how the development has been financed, should therefore not be taken into account when determining the commercial or non-commercial nature of that activity" (Recital 18).

Similarly, "the mere fact that an open-source software product with digital elements receives financial support from manufacturers or that manufacturers contribute to the development of such a product should not in itself determine that the activity is of commercial nature" (Recital 18).

For more information on what does trigger manufacturer obligations, see What criteria determine whether an open source project is in scope of the CRA?.