This device is going to get at best around 2 years of proper security updates due to using an SoC launched in late 2020 with 3 years of support. They're claiming they'll be providing something they won't really be providing without doing the work for it.
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Work is ongoing to get postmarketOS running with the mainline Linux kernel. This will basically mean support for as long as the hardware is functional.
wiki.postmarketos.org/wiki/Fairphone
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A large portion of the updates are for firmware and won't be available anymore after end-of-life. Using a mainline Linux kernel doesn't imply that the drivers are actively developed / maintained either. It just means that the core kernel updates can keep being applied longer.
A device that's only going to be getting 2 years of full security updates shouldn't be advertised as having 6 years of those ahead of it as if it's an iPhone. They haven't done the work to achieve that at all but they're taking credit for it and selling the product based on it.
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