As of 2024, homosexuality is de jure illegal in the UAE.

By January 1st, 2040, will at least one public gay pride event legally take place somewhere in the UAE?

An event declared illegal by the government will not count. If the government is aware of the event and let it happen, the question will resolve as yes, even if at the time homosexuality might be de jure illegal in the jurisdiction. Events happening in diplomatic representations will not count. The event has to be open to the public, so, for instance, a private celebration by residents at their home will not count.