Text Message Forwarding not showing up in settings
Important in cases when the Text Message Forwarding is not showing up in your iPhones settings:
in iPhones' Settings/ Messages/ Send & Receive
make sure you have your actual phone number selected under " You can receive iMessages to and reply to and reply from", not an email or iCloud account address.
In addition you may need to restart your devices and wait few minutes for this settings to take effect and be able to use the text messages forwarding features between your Apple devices.
iPhone SE (3rd generation)