There is a Netflix series called 野武士のグルメ and translated as Samurai Gourmet. I know there's an adaptation because many places outside Japan knows the Samurai word.
Is these words in Japanese interchangeable? Which is usual to use?
侍 is a 武士 who has loyalty to a lord while 野武士 is one that doesn't have that relationship. So they are basically not interchangeable.
That said, it's not impossible to figuratively use 侍 to refer to those people. (武士 is called samurai in English, which looks a constant figurative use of the word from a Japanese point of view.)
Here 野 is a character that means "stray", "wild" or "feral". 野武士 (aka 野伏) refers to unofficial worriers who were more like guerrillas or bandits (and sometimes mercenaries) in modern terms. It's not interchangeable with proper 武士 who belonged to the noble class.
