I did everything to try and get Sanctuary to grow, but despite ample water, food, defense, decorations and stores and 82% happiness the population never goes above 13. Is it because I took the castle mission? Not sure how to grow the population, would appreciate any help, thanks! Edit, my Charisma is 8 and one of my other settlements has 21 people!

I heard the pop cap was 10+ what ever your charisma level.

Charisma+10. Effective (stable) cap is 20. You can wear things that increase your charisma, which will allow for more settlers to come... but extra settlers will also leave if you take it off.

If your charisma is 3... well, that's the reason why.

Nope, my Charisma is 8 and I have 21 people in my largest settlement. I wear clothes that increase my Charisma which is why. But Sanctuary just never grows!

I heard this too, but I can attest it's not accurate. I only have CHR at 5 and have 18 people in my settlement at Sanctuary.

Not sure what the cap is, though. I've seen videos with people having more than 20.