Used pixel actually limit a lot the choice. I've not dived into de-googled phone yet but from what I understood postmarketOS seems like the used/old phone OS

I've never investigated for iPhones but would be curious

1. if they exist
2. how bloody hard they are to get going

I can only speak for laptops/desktops and it being a bitch.

There's a reason I'm very adamant at hating Apple for a multitude of technical reasons. This is but one of them. It's a shame too because their build quality is really S-Tier.