Can't save meeting from .ics attachment to Apple Calendar

To save a meeting invite to your iOS Calendar that you received as a .ics attachment via a third-party email client like Gmail, Protonmail, Yahoo Mail etc.

You must either:

1. Option 1: Set up your third-party email within the iOS Mail client and use the iOS Mail client to click on the .ics file which will add it to your iOS default calendar.
2. Option 2: Forward the email to your apple email and click on the .ics file from the iOS Mail client which will add it to your iOS default calendar.
3. Note: Once you click on the .ics file you will be prompted to add it to the default calendar that you have configured on your iOS device.