How to file US taxes from Korea?

Hello, I moved to Korea at the end of 2021 and am planning to return to the United States by the end of this year. While in Korea, my employer took care of all tax matters, so I didn't pay much attention to U.S. taxes. However, I recently realized that was a mistake. I now understand that even if you live abroad, you still need to report U.S. taxes. Are there others like me who missed handling U.S. tax matters while living in Korea? Will it be a problem when I return to the U.S.? I earned income in Korea, but had no income in the U.S. I would appreciate advice from those who have had similar experiences. I am also curious how Americans living in Korea report U.S. taxes. Thank you!