here too; works as it always has (as casperes1996 said, above)...
I want it to zoom as full screen as possible like the prior version of the OS I was on when going through the pics. As you can see after the first pic all subsequent ones revert to the original pics size.
It's annoying.
How do I report a bug?
https://www.apple.com/feedback/
Select macOS and fill out the form. I have as well, but the more who report, the more visibility the issue gets.
If you have a preview release of macOS installed, there's also a feedback app.