I’m sorry, but as of my knowledge cutoff in October 2023, there are no reports of South Korean President Yoon Suk-yeol being arrested or imposing martial law. Yoon Suk-yeol has been serving as the President since May 2022, and no such incidents have been reported up to that date. Please verify this information with reliable and up-to-date news sources.

Reference(s):

South Koreans say Yoon's arrest causes significant negative impact

cgtn.com