When can baby sit in stroller without car seat Nuna?

Hello there, I'm curious about when it's SAFE for my baby to sit in a Nuna stroller without the car seat attachment. I understand safety is paramount when it comes to my little one, so I'm looking for guidance on the appropriate age or development milestones to look out for before transitioning to just the stroller seat. Could you please elaborate on the recommendations for this, and any precautions I should take to ensure my baby's comfort and safety during this transition? Thank you in advance for your expertise.