Problems with posting photos

Can anyone explain why I cannot add photos into my posts from the "photos" library on my Mac Notebook pro.

I have taken some digi-scoped photos with a Lumix G80 camera and telescope, put the card into my Notebook and downloaded them into the "Photos" library.

Next I tried to insert some to my Blog posting, but when I click on the Blog picture link it brings up a l.h sidebar with a choice called "Pictures", choosing this doesn't bring up any photos from my library but does bring up old photos (from 3 or 4 years ago) via Google photos, I don't know why there are any photos in Google in the first place.

Does anyone know what is happening here, I have obviously missed something! not that that is unusual.