I just figured out a way how to post photos from Google Photos. I'm not endorsing the site mentioned below. It's just what I found helpful...
1) Create a link to your photo
2) paste the link onto https://ctrlq.org/google/photos/ as instructed
3) copy and paste the "Direct Link (URL)" that is generated from the website into your post
4) type
after the link
Just saw you post now. That's what I did for my trip report.
All my pictures are automatically uploaded to my (unlimited) Google photos account with the
original size, so that's the best option for me.
You can also change the size of the picture by changing at the end of the link the width (W) and height (H), like "w1415-h944" replacing the "w2400" that come by default.