This is why threat modeling is important.

but what if I get arrested on some false pretenses and they use cellebrite to gain access?

Chances are they can clone the eMMC and wait for a CVE. Or threaten or hold you until you cave. If a lawsuit is your only recourse, I would expect any constitutional barriers to be ignored in practice. Your best bet is to never end up being an explicit target, which may be more difficult for certain individuals.

My threat model considers dragnet surveillance as the primary threat, so I’d compromise on surviving dirty maid type attacks in favor of reducing the information my device gives out.

Obviously if your device is being actively exploited, you cannot be private. But your security requirements increase greatly if your data footprint indicates to them that you warrant targeted scrutiny.

GrapheneOS is also open source. Fairphone could realistically fork the project without meeting the requirements deemed necessary for the maintenance effort by upstream.