When entering PIN for the SIM card during bootup, nothing appears to happen after pressing the ✓ button for several seconds if the entered PIN is correct. Would be nice to get some feedback.
True. On earlier devices SIM input was semi-immediate so there was no need for extra feedback, but on some specific newer devices there is a notable delay that would benefit from some kind of visual indication (also slow registration should not block user from continuing to other tasks). Ideally the delay gets fixed in hardware adaptation level, and not worked around on UI.
The UI could at least show the spinner while waiting, so you know that your input is being processed.