Baby’s sitting up unassited with a curved spine?

If your baby is able to sit up unassisted or somewhat unassisted, do they have a slight curve in their spine? Like leaning forward a bit of a C shape? I’ve heard this means they shouldn’t be sitting up for long periods of time as they haven’t got stable enough back muscles yet. So a minute or two here and there is fine but like in chairs for ages to eat etc, probably not?? I dunno?? This is info from various countries paedtrician a and physical therapists 🙈 So when do I start weaning? Cause they always say by 6 months but only 30% if babies can sit up with straight back by 6-7 months lol. Majority are around 7-8 months! I’m so confused. Either way, forget weaning; so I shouldn’t be putting my baby in forced sit up positions for long periods of time because she has a slight curve still?? I have no idea!?🙈😅