Actually, nothing was removed, but something was added! If you look at the screenshot in the first message, you will notice that Lightroom offers you to go to 'Locate File', but also to 'Locate Folder' (if the folder of that image is also missing, that is). This is even the default button and this is new for Lightroom Classic 14.5. Previous versions did not point to the missing folder option, you would have to look for that in the folder panel yourself. Maybe this new dialog is what causes the confusion about the aleged (but not really) missing 'Find Nearby Missing Photos' checkbox. This is how the old dialog looked:

OK, I finally had the chance to do a quick test on my Mac, running MacOS 15.6.1 and Lightroom Classic 15.4.1. I cannot reproduce any of the compaints. Nothing has been removed and nothing does not work on my system, so there is no bug. The 'Find Nearby Missing Photos' option is at the bottom of the dialog that you use to select the missing photo (where it always was), but you'll have to click the 'Show Options' dialog to see it. Maybe the latter is new, I don't know. It was checked by default, and worked as expected. Selecting the one photo reconnected all of them.
