Why is my dog not eating his food but will eat treats?

i’ve got a 2 year old golden retriever who’s suddenly gone super fussy with his food. he used to eat fine but now just sniffs it and walks off, yet he’ll happily eat any treats i give him. i’ve tried changing brands and mixing in a bit of wet food but he still won’t touch his kibble unless i hand feed him.

he’s otherwise happy and full of energy, just not interested in proper meals anymore. anyone else’s dog done this? not sure if it’s just him being stubborn or if i should be worried. any tips?