Could you add something saying explicitly what a timestamp _is_ under your terminology? Is it an integer offset from the UNIX era start?

It's an abstract concept. It's nothing more than a given point in time.

How you represent it doesn't change the definition. It could be stored as the number of seconds since some arbitrary point in time, such as Unix timestamp, or a Julian timestamp.

Or, it could be a given time and date combination with some fixed point of reference, such as UTC. I'm sure we all have favourite ways of representing timestamps.

Ok, one thing — perhaps not the most important — is that “timestamp” is a very unfortunate terminology for the abstract concept you describe. The word timestamp very much suggests that it’s referring to an explicit representation of some sort. “timepoint” would be much better for what you’re talking about. Not a criticism of you of course! I mostly write python at work so I rarely am directly exposed to the integer offset values, but I know many people use the word “timestamp” to refer to that integer, as opposed to a formatted string. Which also seems like unfortunate terminology, since what is a stamp if not formatted?

You are assuming that timezones don't change ever in relation to UTC. This is wrong. Timezones change all the time.

When I set an alarm for any time in CEST in 2022 and convert this to UTC before saving it, it will very likely ring at the wrong time, simply because CEST will probably not exist by then and be replaced by CET due to the EU getting rid of DST.

But an alarm is not supposed to use timestamps. An alarm is set for a certain time in a certain location. In otherwords, a wallclock time. Not a timestamp.