You're planning on soon transitioning from a 2 year old phone for sustainability reasons?
I'm currently leasing my Fairphone 4 from Commown, so I'm fairly sure it will go on to live a healthy and productive life elsewhere. I also purchased a used Pixel 6 Pro from eBay.
As per my comment elsewhere in this post, I'm switching away from Fairphone because I care more about the security and software-level ownership of my device. If GrapheneOS had support for Fairphone, I would have stuck with my FP4 for many years to come.
> ... most straightforward ROMs I've used ...
ahem I believe GrapheneOS is an OS, and not a ROM... The project founder really wants you to use the "right" terminology: https://news.ycombinator.com/item?id=33567842 ;)