I've been in the painting business for over twenty five years and have
never heard of a paint with paste consistency that fills paneling
grooves, BUT, that doesn't mean it doesn't exist. I prefer to use an
oil-based wood primer (NOT KILZ) followed by two topcoats of satin or
semi-gloss oil based paint. The grooves look fine. I have used spackling
before to fill the grooves but for the time and effort, it would be
better to remove the paneling. HTH