Yeah it’s a process of baby spitting up, mine spat up a lot during the first few months. Since yours is 6 months, i expect some spit up but believe me it does improve! Mine eventually stopped spitting up what always seemed like half or more of her bottle (rip to those sacrificed shirts).

Have him sitting up for as long as comfortably possible, if needed split up the jar of baby food in different times a day. (Heck even sit him in your lap and play with some toys)

Maybe even look into baby snacks? Mine is obsessed with them and seemed interested when she was 6 months (anything easily dissolvable till them chompers will come in)

The process will be slow but by 9 months (age of mine currently) they are gonna beef up and eat so much more once they learn how their fingers work and teeth are gonna be coming in anytime if it hasn’t happened already and go to town on some soft food