iPhone Timer doesn't sound if period is the same as screen lock timer

The Timer on my iPhone doesn't sound if the period is set as the same period as set in the screen lock timer. If you don't touch the phone in between you will miss the timer end.

This was already reported in 2020, but Apple just gave some lazy standard reply here à la "restart your phone" instead of taking this seriously and really solving the bug:

iPhone Timer doesn't sound if period is s… - Apple Community