Yes i noticed. It’s not there anymore. One work around is possible if you have a Mac with older mac os (13.6 or earlier). This may / may not work in mac os 14. I haven’t updated.
And for this you need to have your photos synced with icloud.
Open photos app on mac. Edit the photo. There u will see magnify in markup tool. And an option to hand off to iphone. The same image will appear on iphone with older markup tool options. Including magnifier.
hope apple brings back markup tool - magnifier option. The ios 17 guide mentions magnifier in markup tools. But actually its missing on iphone as of now.