The lock screen won't show anything sometimes, and you can't unlock it. It's just a wallpaper. I had to enable face unlock and auto unlock in order to use the phone. It start the camera app with the power button, try to access photos frying there, and that gets the fingerprint to work and unlock it.

> What are the worst issues I am likely to encounter?

Complete loss of data. https://arstechnica.com/gadgets/2023/10/android-14s-ransomwa...

Back up your data while you can.

I've noticed that tapping notifications has a significant delay (350ms or so) before it opens any app since upgrading to 14.

If you use multiple profiles, you could potentially end up somewhere between locked out of your main account, to even soft- and hard-bricked. See siblings link from Ars.