I decided to see if the new folding fingers from the GoPro HERO13 are backward-compatible with older cameras, despite saying they are not compatible. It looks like a solid "maybe" and "it depends".
Here's my HERO9 with the new HERO13 folding fingers, with its fancy magnetic latch and 1/4-20 mount fun.
https://gopro.com/en/us/shop/mounts-accessories/replacement-folding-fingers/AEMFR-002.html