Here is the URL (I don’t see where I can submit a screenshot):

https://55o.8a9.myftpupload.com/service/

Here you’ll see that I have set a Featured image displaying at a constrained 1520 x (?) px wide, and an embedded Vimeo – original size 1920 x 1080 – but also constrained to 1520 x 855 px.

Where is this width adjusted?

Yes, this is what I want to adjust.

Thank you for your help!