Supporting an alternative OS wouldn’t change the fate of Fairphone, imo. Most people don’t care to move away from the stock version of Android that comes with their phone or iOS.

I mean, aside from /e/OS as a first-party option, there are also official Lineage builds[1]. And they're at least a target for PostmarketOS[2], even if that wiki doesn't actually describe something daily-driveable yet.

[1] https://forum.fairphone.com/t/official-lineageos-23-for-the-...

[2] https://wiki.postmarketos.org/wiki/Fairphone_(Gen._6)_(fairp...