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.
This is especially annoying for screen-based projects, since the fixed page spacing seems to be in mm, not px.
Here's my solution:
- Get a guide at the end of the previous page.
- Double-click the guide to change its origin.
- Set the coordinates the next page should start from.
- Drag the page until it snaps with the guide origin.
It's also very annoying when working with grids, as they never match the origins of the new pages (unless your grid is based on the gap between pages, which is never my case, as I use the metric system or pixels). I don't think the gap is defined in mm; I measured the default gap and it is 2.646 mm, a very odd number.
Nevertheless, it's still awesome to have multipages in Inkscape.
This is how I deal with it:
- set the grid and guides in the first page
- always keep this first page as the working page
- after laying out the page, create a new page and move the objects to the new page
- align the set of objects to the left of the page
- displace the set of objects horizontally by the value of the desired left margin
- after creating all the pages, save as PDF starting from page 2
I always keep the working page, in case I need to make further pages in the future. If I need an SVG with only the finished pages, I save it as a new SVG file and delete the first page.
BTW, it would be great to have the option of defining the gap between pages