Yes. Here's the guidance that appears the first time you use the citation dialog:

After you've made your selection, click the bubble or press Cmd-↓ to add page numbers, prefixes, or suffixes. You can also include a page number along with your search terms to add it directly.

(It's Ctrl-↓ on Windows/Linux.)

If you open the popup, you can Tab/Shift-Tab between fields. (There's an open ticket to make it focus the page number field automatically like it used to.)

As it says, if you want to add a page number, the easiest thing is to just do that as part of the search string. If you want to do it while editing a citation without opening the popup, it's also possible to just type "p123" if you move around first with the left/right arrows, but the left/right part shouldn't be necessary, so we'll try to fix it to allow you to type "p123" immediately after bringing up the dialog.