For
Royal Caribbean, the MDR (main dining room) is free for dinner, and at least sometimes lunch. It used to be open for breakfast, but not sure that's returned since Covid.
There's also at least one Buffet (Windjammer) on every ship, that's open for Breakfast, Lunch, and Dinner.
There's a free pizza place (Sorrentos) I think on every ship, as well as Cafe Promenade (small sandwiches, some small deserts, and coffee). Cafe Promenade is 24 hours I believe. All the rest have specific hours.
On larger ships, there's more free choices that will depend on which ship. DW & I have been on four cruises, only purchased Specialty Dining on our first (the package price for three dinners was pretty reasonable), that on Oasis of the Seas.
Of course, a LOT can change in three years.
I suggest first deciding what itinerary you want to go on... Caribbean (Eastern, Western, Southern), Alaska, West Coast, Europe, etc, then think about what size ship you want (some of them, the ship is as much a destination as the ports). Once you have those narrowed down, THEN look at dining. Unless something drastically changes, you're not going to go hungry on a cruise (unless you want to).