I just loaded Photoshop 22.3.0 and, as usual, odd things have changed. My ACR version is 18.104.22.1688 In ACR, the Zoom tool toggles between zoom in and zoom out with each click. Only one level of zoom can be achieved. The Crtl+ and Ctrl- shortcuts operate as expected, but the Zoom tool itself does not operate correctly. The Zoom tool does work correctly in Photoshop's normal window. The problem appears to occur only in ACR. How can I get back the Zoom tool behavior that existed in the previous versions?
I think it was around Camera Raw 12.3 that Adobe modernized the zoom tools for Camera Raw and Lightroom Classic so that they have more flexibility and options.
I’m having a tough time finding out where Adobe documented it in the online User Guide and release notes, so this is off the top of my head:
To toggle between Fit view and the last preset magnification, click the Zoom tool. This is what you already found. One magnification of that toggle click will always be Fit, but the other you can set by choosing a magnification from the menu near the bottom left corner of the Camera Raw window. For example, if you choose 100%, clicking the Zoom tool toggles between Fit and 100%, and if you choose 400%, it will toggle between Fit and 400%.
This one’s my favorite improvement: You can now do a continuous zoom by dragging the Zoom tool left to zoom out, or right to zoom in. Because it is continuous (not stepped), you can now get any incremental zoom magnification you want, depending on when you stop dragging. If the Zoom tool is not selected, you can temporarily switch into this mode by holding down the Command key (Mac) or Ctrl key (Windows). Whatever magnification you last set using this method is another way to set the non-Fit toggle magnification when you click the Zoom tool, so if you last continuous-zoomed to 228.7%, clicking will now toggle between that and Fit.
If you want to drag a rectangle around a specific area you want to fill the window, Command-drag (Mac) or Ctrl-drag (Windows) the Zoom tool.
Some of those might not work if your graphics hardware isn’t supported under Camera Raw Preferences > Performance.
The current keyboard shortcuts for zooming are under the View menu.