The OP6 works decent enough for my needs atm. I use it for matrix chats on fluffychat, browsing with firefox works well. I can use it as terminal client which was important to me since I have some servers that I need to work on remotely sometimes.
So far I havent realized my idea to use it with a usb/hdmi or DP adapter as a mobile computer but thats something I‘ll try.
So far I havent managed to put a sim card in it since I dont have a spare and my old phone still works so I‘ll get to that at some point.
To your problem:
The pinephone is open source. You can look in the schematics and check if the motherboard gets enough juice and what if anything is broken afaik. The pinephone is not an end user device imo, the OP6 very much was but postmarket isnt. The documentation of the pinephone should also be somewhat extensive.
So I‘d suggest you either stick with graphene or start embracing the tinker mentality. :)