I got a Fairphone 4 after security updates were discontinued on my Samsung Galaxy S9 and I figured out it couldn't be flashed with a new OS (it was a fantastic phone while it lasted- was honestly Underutilizing its overall power. Got 5 years out of it).

TLDR : read the last paragraph

I am honestly taken aback by the transparency in regards to the FP4's construction. The repair manual gives the part number, quantity, and purpose of every single component on the PCBs. You get the full schematics as well.

Obviously I can replace any major part/board until support stops (they're saying they'll support it for 3 more years minimum), but I imagine that I could stock up a couple spare parts and treat the device well and get much longer from the hardware. As for support for the OS, I got the phone through Murena who put their own custom OS on it, but I imagine I could flash a new OS onto it without much problem.

The things I am thinking about are past that point. If replacement parts no longer get sold and something fails on one of the boards, I don't know the feasibility of finding a replacement component. Like, I imagine getting a matching capacitor wouldn't be an issue, but can you even find a replacement snapdragon or WiFi chip? And while we're talking about hot-air soldering on replacement parts: do PCBs have a duty lifespan? Is it more likely that my screen'll just die long before anything else?

Basically, assuming I treat this phone right and don't break anything in a drop, how long can I glide this fella out? what's the shorest lifespan parts that'll fail first - and what kind of lifetime can I suspect? What are parts I could consider replacing with a similar part? (I own a 3d printer and do diverse material fabricating as a hobby).