EUSS family permits For Non EU child UNDER 21

Dear friends
I came in 2014 with my EU passport
My wife and two child Came in august 2019 on EEA non-EU family member permit
My third child still in non EU country who age 18 now
My questions is after 30th June 2021 can I sponsor third child ?
Secondly I have to give explanation HO why my third child not came with other family member who’s came in 2019 ?
Do I need to give extra evidence which can prove my third child still there ?
What category use for application my third child ?,last my other family member came on EEA family permits If I sponsor now I have to use same category ?
Anything other suggestion which can improve successes chance of entry clearance visa issue that would really helpful
Thank you all.