Generally, Paramount owns all Star Trek IP rights.

However, reusing some things isn’t cost less. In some cases, they have to pay residuals to specific individuals or subcontractors who have creative rights.

Historically, this has led to weirdness such as renaming the Locarno character from the TNG episode ’Lower Decks’, played by Robert Duncan McNeill, to become Tom Paris in Voyager because Paramount didn’t want to pay the writer who got scrip credit for the TNG episode ongoing residuals for creating the character.

I don’t know enough about whether creators of animated character designs have rights to similar kinds of residuals, or the production houses like Titmouse for Lower Decks, but one has to wonder. It was so strange that Paramount+ suddenly said it was refocusing away from animation just as Skydance started its moves to acquire it.

Protostar is Nickelodeon, but I don’t see any reason the Cerritos couldn’t be used.