I don't think you should worry about this really, they all seem to do things at very different times. My little one is nearly 14 months and he only stands for a few seconds unassisted, and then falls on his bum. He actually won't let us help him with standing/walking at all and will only move around using his walker or the furniture to hold on to. He's only just started to try and stay standing up while not holding onto something.
Do they stand up when like leaning on the couch or cruising at all? I don’t be worried or fully bring it up until 18 months but I think you could call your babies doctor and ask maybe. But I’d also just help baby stand and help them get leg muscles
I wouldn’t be worried yet they all do things in their own time. My baby is 13 months but he showed 0 signs of standing then stood and took 5-6 steps within days of each other about a week ago so there isn’t always a big build up. I also have friends who’s LO’s never stood unassisted and just got up and walked! x