Earlier quoted context omitted.
The user interface can be akward, but you can ask them for the timezone of the event. If it's for a live event in another place, they would ideally put in the local time in the other place and the timezone there. Or if it's a fixed time, not to be moved by DST changes anywhere, they could specify it in UTC. It's also a good idea to calculate and save the offset when editing. Then, if the offset changes later, you can…
I can’t even get employees at the company where I work to understand and communicate EDT instead of EST. I don’t think calendaring tools are going to have much success asking people what timezone they want.
Which is often what we want!
So on that regard, I find calendar invites rather than a causal email invite to be essential.