Feature summary (what you would like to be able to do and where):

The dropdown is extremely(!) long. Would be very useful to have some autocomplete. For example: after typing "War" I should see a short list with at least "Europe/Warsaw" as one of the suggestions.

I want to clarify that the list should get shorter when you type. Same as here when you type "av" or "scr".
https://jqueryui.com/autocomplete/#combobox

I assume this is something you would want to implement in OOUI, so tagging as such.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

I reported this for Events function. You have to choose a timezone each time you create an event.
I was told that the timezone selector is a more generic thing... So would also be useful for Preferences too.

Benefits (why should this be implemented?):

Creating new events would be easier and more enjoyable.