Google Pixel phones for a while have been the phone of choice as they allowed easy root and bootloader access. Not sure if that's still the case, though, as they've been pivoting.

Other manufacturers offer it as well — these options continues to exist, and while it's certainly not a high percentage of the market, some of these phones sell because of openness.

Niche manufacturers usually focus on "stronger" openness (Librem, PinePhone, Fairphone...) — but they provide subpar hardware compared to mainstream top-end. Eg. most recent release in Volla Quintus (https://volla.online/en/volla-phone-quintus/) uses SoC that is half the speed of Google's Tensor G4 in both single- and multi-threading benchmarks: https://www.cpu-monkey.com/en/compare_cpu-mediatek_dimensity...

So I generally go with phones which can get their bootloader unlocked and which can be rooted, to ensure I have full control of them. I did, in the past, use Ubuntu Phones (Meizu MX4, Nexus 4), HP/Palm Pre Plus and 3 (webOS with full root access), Nokia N9, Motorola A1200 etc — all as my daily drivers. I did get PinePhone, but that thing is sloooow. Since, I've switched to plain Android phones which allow you full control.