Great! The URL worked! Thanks! That search method gives me the expected number of results. Next is studying exactly which tables in the database have contact/group/contribution/activity info, and just copy those, so that hopefully the new instance of Civicrm won't have these weird problems. Presumably, at some point, I screwed up some upgrade.

Unfortunately, I don't have "include / exclude" custom search, nor does the API explorer work properly. And yet my site is using 5.27.0, released July 1st 2020, so I don't think that is excessively old? When I select the dropdown by "Required", there is just the options "Optional" or "Required". And the box with the title "On" doesn't appear. I also have some problems with double menu entries, and basically it seems like at some point something with my install screwed up, so why I'm trying to clean up the data and move it over to a new install...

I am using Drupal. I'll look in to webforms. I have to admit that I use Drupal for CiviCRM but our organizations main webpage is separate, using TypesetterCMS, so I'm not so deeply familiar with Drupal functionality. I have thought about combining the two websites, as it would look a lot better, but migrating will be a big project for me.

That was the right file. :-) Actually, line 282-290, which checks for the cookies signed_ and confirmed_ I commented out. I ended up leaving the two lines about redirectIfSigned alone-- they seem like they don't matter since I have the petition profile set to create duplicate contacts for now.

Thanks for that information. Looks like a lot to get my head around! I guess I could have searched it out. I don't think it was so well documented the last time I looked for it (possibly 5 years ago).