As far as I know, I don't think there is currently an easy way to change the gap spacing and get them all exactly the same, at least not automatically. The default gap for new pages seems to be fixed, and I can't find any option to change it. The multi-page feature is very new to Inkscape 1.2, so they might be able to improve it in time.
The Align and Distribute tools don't work on pages. If they did, then this would be the ideal solution. Sadly not. You can't currently select multiple pages with the Pages tool, only one at a time, so that's probably why it won't work.
I have noticed you can use the Alignment option in the Snapping Options to align pages using the Pages tool, but unfortunately the Same Distance option doesn't appear to work on pages. Would be nice if it did, but it doesn't. Perhaps you could make a feature request on Inkscape's gitlab bug tracker.
The Same Distance alignment option in snapping does work very nicely for objects on a page, though.
Using a grid, with snapping turned on, and moving the pages manually is probably your best bet to be honest.