Screwing into grout

[M16]

How heavy are your knives?

I'm guessing with the magnetic bar it will be four pounds exactly.

[cbd10pt]

If you have sufficient surface area 3M double-sided tape will hold.
If not drill a 1/4 inch hole use a plastic anchor. One of the newer ones that acts like a toggle bolt.

I make my living remodeling I would go one of these 2 methods