Apple announced at the 49th CA/Browser Forum on February 19 that it will limit the term of accepted TLS certificates to 1 year (renewals: maximum 398 days) as of September 1st, 2020. Certificates issued on or after that date with validity beyond 398 days will be distrusted in Apple products.
Certificates issued prior to September 1st, 2020 will have the same maximum validity as certificates do today, which is 825 days. Valid two-year certificates will operate correctly for their full duration, even after September 1st, 2020. No action is required for these certificates. Certificates, if being issued after August 31, 2020, will need to issued for 1 year to remain trusted in the Apple platform.