Oooh!
The original [ window.history.back() ] version worked for me, whereas the [ $('.nav_btn')[1].click(); ] suggestion went back to page one of the bundle each time. It would then grind back to the right page and continue, but it was adding serious runtime and consequent CPU usage.
It is currently doing the Bundle for Racial Justice and Equality for me. It got stuck at one point - some publisher removed three games from here and the script can't cope with the resulting error pages. Fortunately, they were all on the same one of the fifty nine pages of items, so it was easy to do the remainder on that page manually then resume the script on the next page.. and I see it's just finished.
Thanks to you and, of course, the author of the original script.
Itch really should do this automatically with a single button click, of course, but hey ho...