Don’t confuse constructing a date with formatting a date. You can format a date in UTC natively in Bubble (:format as… select timezone using static timezone UTC [or any UTC equivalent]).
NOW, if you’re trying to trick the user into selecting a date in UTC, that’s a slightly different issue.
But a date, once constructed, is just a date and it is the same for all users everywhere, regardless of how you present it to (format it for) the user.