rambleon Glad you got it fixed--what you're describing is a separate issue, known for pixels dating back at least to the 6 if not earlier, with or without GrapheneOS or stock Android. That issue basically has to do with the phone needing more power to boot than it can negotiate from the charger, so if your phone gets discharged too much, it will end up in a loop of trying to boot immediately after charging, discharging too fast, shutting down, etc.
The solution can be to use a Qi charger, as you found, or just to interrupt the boot (if you have GrapheneOS, at the stage that you see the screen, "Your device is loading a different operating system", just press the power button) long enough to let it charge (e.g. 30 minutes), then let it resume the boot. You could also call up the bootloader with the Volume Down + Power buttons, let it charge, and once it's got sufficient reserve charge, boot normally.
Alas, I don't think that's our issue here (I did try a wireless charger for my P9PF, to no avail). But it's interesting that a lot of Pixel 9 Pro Fold users (stock OS and Graphene) are reporting hardware issues, especially recently. Probably the Pro 10 fold has a more robust hinge