Apple announced at the 49th CA/Browser Forum Face-to-Face that it will limit the term of accepted TLS certificates to 398 days as of September 1, 2020. Certificates issued on or after that date with term beyond 398 days will be distrusted in Apple products.

Certificates issued before that date are not affected and do not need to be replaced or modified—you can continue to issue 2-year certificates until August 31, 2020, and use them until their expiration. This announcement was made by Apple on February 19th at CA/Browser Forum, an industry standards group meeting.

https://support.apple.com/en-us/HT211025