GrapheneOS on a Pixel is probably the most polished and secure experience.
I have installed it (and enabled sandboxed Google services) on my mom's phone (she's pretty non-technical) and she had no bigger problems in the last years.
Before that I was using crDroid on a Poco F3 (I switched because the camera was quite awful and the battery got drained rather fast), and I was expecting some of crDroid's features that were just missing. A shortcut to the flashlight via power button long press, battery charge limit/smart charging, bandwidth display on the status bar, the option to add more columns to the quick settings, just to name a few.
I ended up running crDroid on the Pixel as well, overall it's a decent experience, but not nearly as polished, it turns out I had to manually grant Google Play Services the location permission via ADB so apps would know where I am (missed a train to that one).
I'd love it if there was some ROM that combined the security and sandboxing from GrapheneOS with all the neat little features in crDroid... or an actually good Linux phone.
My personal hill to die on is that the launcher uses lil tiny icons and text, which I find hard to read, and alternative launchers are a bit of a privacy and security disaster. They refuse to add anything to the built in launcher to adjust this, and suggest either raising all of the sizes (with accessibility, which affects all apps) or use an alternative launcher.
Alas it is still a very nice operating system.
> Why is the recent screen buggy?
> Unfortunately, it is because the system launcher handles the Recents screen. Therefore, if you change the default launcher, weird things can happen [...] The only way to fix this is by having a Magisk module called QuickSwitch.
https://lawnchair.app/faq/#why-is-the-recent-screen-buggy
(Can't vouch for the accuracy of this information as of $CURRENT_ANDROID_VERSION.)
Someone with a threat model that GrapheneOS addresses could always use access to a quick flashlight.
However I've found that flashlight is still relatively accessible. It's three actions - press power, drag finger down from top of screen, tap Flashlight. Not too bad, but not possible from muscle memory or with gloves on. Good for looking under the seat for your keys at a movie, bad for quick reactions.
When I'm traveling or outside at night, I tend to carry a dedicated flashlight, but I'm odd like that.
With one exception. The couple of times I've called emergency services, they were not able to detect my location since GrapheneOS does not support the protocol for this. So, I had to waste time giving directions. It's a tradeoff for privacy vs safety.
It might be something to think about before, say, putting this on someone's phone who has a medical condition or is elderly.
Some shown here: https://lineageos.org/Changelog-28/