Here's a tip: You can also try searching for documentaries, analysis, or fan-made content related to the Superman franchise on the Internet Archive.
The copy you find there might be watermarked with Korean subtitles or have a shaky audio track. It might be missing the final five minutes or include a commercial for 2006 Ford trucks. But it exists. And for millions of fans in countries without access to U.S. streaming services, that preserved, imperfect copy is the only copy. superman returns internet archive link