Physical keyboard

Human coded Smart Keyboard. Ever since they changed to learning algorithms the spelling and grammar corrections have gotten much worse.

Ability to automatically turn wifi on and off with screen.

Samsung had a little pressure sensitive area at the bottom of phone screens in the S9 era. It was handy and I had it set up like a hidden home button.

The S9 also had a variable aperture camera, which I feel like could have been developed a lot more.

I also miss notification LEDs. Sure, AOD mostly replaces it, but it was fun setting different colors for people, situations, etc

The Essential phone had a ceramic back that was very comfortable and cool in the hand. Though it was slippery. Another idea that could have been developed further.

The different back materials on the Moto X were very satisfying. The customization of that phone was unmatched!

I think this is a One UI 7 thing, but the battery indicator for connected Bluetooth devices has completely disappeared. The only way to check the remaining battery life of my connected headphones or speakers is through a third party application, I can no longer find a way to do it in the OS itself.

Yes, that one right there in the picture.

Reading through this thread gives me serious nostalgia. My first smartphone was a Motorola Droid, which really had it all: physical slide-open keyboard, headphone jack, removable battery, configurable notification LEDs, shake guesture for the flashlight. Good times. Kept on running with CyanogenMod well beyond the official support.

I got Motorola with a headphone jack, and I use it surprisingly often. All my Bluetooth stuff has fallen apart faster than my wired stuff.

The 3.5mm AUX jack.

higher dpi/4k screens.
oled pixel layouts already have fewer subpixels than they should for say a claimed "1080p", leading to weird blur or aliasing in places.
My high dpi phone has made my eink reader redundant; the sharpness simply makes it way more comfortable to read, for me enough to be on par with print.

And now I can only await how long my phone will remain usable, knowing no new phones with higher dpi (600ppi+) are being made.

Rectangular screens without missing parts. I hate rounded corners.

Wild cards for number blocking. You could block whole area codes. Goddamn worthless fucking Nazi bastards took it off.

Trackball

I used to be able to ~~unlock~~ wake my phone and see what band was currently playing.

OneUI fucked that up.

Edit: wake

• pressure sensitive pens on non-flagship models