Unfortunately, the Pinephones are gradually losing out to ex-Android phones (such as Oneplus 6/6T). Less and less hackers work on it. As a result, Mobian nearly dropped all support for it. Even postmarketOS has recently demoted it from the prestigious 'main' category it has been in for years. It is very likely that the next 'main' devices will be the Oneplus 6 or something else with that SoC (sdm845)

A large part of the PP drivers have been FOSS, yes, but in a manner that is not aligned with Linus' tree. i.e. a lot of those drivers simply could not be accepted into Linus' tree. The situation is a little better now, but there is still a long way to go, and with developers slowly turning away from the device, it will have to be seen how the long-term fate of the PP works out.

I am not sure why you would imply that the N900 kernel has not made it to the future ... Considering that you can just clone Linus' tree, and build that kernel with zero patches, and have it boot and work perfectly fine (which you cannot do with either PP model).

I maintain the N900 packaging in postmarketOS, and we really have only one patch for the N900 (to avoid a modem-related kernel oops ... i should actually spend more time on it so we just upstream it). The only non-working drivers/hardware is the Bluetooth (and FM receiver, since that's tied to BT). Everything else is working quite well and is very reliable too.

Of course the PowerVR GPU drivers are not FOSS, but they do work on latest mainline kernels. Instead of the state of drivers/kernel, N900 is simply limited by the aged hardware more than anything else, i.e. you cannot, for example, use it for browsing in any reasonable manner anymore.

For funsies, here's me running Linux 6.14-rc2 on the N900 (on postmarketOS with i3wm and tint2 for a bar)