I personally always offer something else. I'm really not convinced that will make them a fussy eater!
Wait until the next meal. He's under 1 so nutrients come from milk still, and I'm not starting the making something else game 😂
I struggle with this too and end up giving him fruit and yoghurt (which I would have given after anyway) when he stops eating and gets grouchy. Worried I give in too easily but otherwise he just shouts at me and gets really wound up trying to get out of his high chair.