According to Apple https://support.apple.com/en-us/HT210176, any private SSL certificate with a term longer than 825 days issued after July 1, 2019 would not be trusted by Apple devices (Safari and Chrome on iOS and macOS)
To resolve this issue, we would recommend requesting 2-year term private SSL certificates in order to get Apple devices trusted.

The most recent test with Apple devices (iOS and macOS):

• Sectigo private SSL certificate is to work on Apple devices and is issued longer than 825 days, the 'notBefore' date must be prior to July 1, 2019.
• Apple enforces the 825 day limit for private SSL certificates on macOS, where the 'notBefore' is after July 1, 2019.

The above tests explain:

• Sectigo private SSL certificate with a term longer than 825 days issued after July 1, 2019 would NOT be trusted by Google Chrome on Apple devices and Apple native browser Safari.

• Sectigo private SSL certificate with a term longer than 825 days issued after July 1, 2019 would be still trusted by Firefox on Apple devices.

For more information please refer to https://support.apple.com/en-us/HT210176

NOTE: Private SSL certificates for Windows are NOT affected.