How can I install or activate an eSIM QR code received on my mobile phone?

On all eSIM-enabled iPhones (starting with iPhone XR & XS from 2018), if you have iOS 17.4 or newer version you'll be able to activate an eSIM QR code received on your iPhone as follows:

1. Long press (long tap) on the eSIM QR code received by email or in app to open a menu (as shown below)
2. Tap on "Add eSIM"
3. Now you just follow the eSIM installation steps from Step 2. (i.e. no need for Step 1 which is scanning the QR code)