My (probably unpopular in general but... actually likely fairly popular amongst this site's intended audience) opinions on smartphones today.
Why notches? WHY? Just because Apple used them doesn't mean every single manufacturer needs to start making their screens have ugly black bits on them.
Really, why Apple at all? They sell uncustomisable and locked-down stuff at higher and higher prices with fewer and fewer nice-to-haves (e.g. headphone jacks) each year. And the vendor lock-in (Lightning headphones, iVersionsOfMostOtherSoftware) is also bad.
It would be nice to not have battery life ruined to get slightly slimmer phones.
The complete lack of updates after a year or so is annoying. Custom ROMs kind of fix this but many aren't available (or even aren't possible due to locked bootloaders) on many devices. This is probably just planned obsolecence.
Most of the stuff manufacturers preload (their own UI skinning, apps) is just useless bloat. Especially the preloaded, unremovable, probably-spying-on-you Facebook apps which are annoyingly common.
The lack of SD card slots is, again, probably just planned obsolecence.
Proper physical QWERTY keyboards would be nice, though as they're such a niche feature that's probably never going to happen except on a few phones.
The screens don't need to get bigger. People's hands aren't growing every year. And they don't need more pixels to drain increasingly large amounts of power.
Removable batteries should come back. When I initially wrote this in 2017 or so, they were pretty common, but now barely any new devices let you swap the battery, despite lithium-ion batteries degrading within a few years of heavy use. I know you can't economically do highly modular design in a phone, but this is not a complex, technically difficult or expensive thing to want.