Girls, hi! I've run into a problem. The baby still can't sit on his ow…

Girls, hi! I've run into a problem. The baby still can't sit on his own, I put him in a feeding chair lying down, but for the last two days he pulls himself up to the bar and sits down, leaning slightly forward, so his tummy is pressing against the bar and sits like that... He started doing this in the stroller too. I put it back, he freaks out and sits down again... Maybe anyone has encountered this? What should I do with him? I don't want problems with his spine later... He can't sit properly yet, I don't even put him in a highchair sometimes, he begs to be put in it by himself, shows me with his hands and