It annoys me that I can't initiate a WhatsApp message to someone that isn't in my address book, so I found a way around it using the "Shortcuts" functionality in iOS.
I created 2 WhatsApp shortcuts, both allow you to easily initiate WhatsApp messages to numbers that aren't in your address book.
Here's my tweet storm announcing this, if you like this and find it helpful please retweet!
https://twitter.com/gshewakr/status/1332573665276223488?s=21
Please follow the steps below to install the WhatsApp shortcuts. This is best followed along on mobile.
Shortcuts is a default app provided by Apple on your iPhone (at least it was for me). If you don't have the Shortcuts app installed, you should install it. You can get it by searching for "Shortcuts" in the App Store, or clicking here:
You need to allow iOS to install shortcuts that have been built by other people. This step allows you to do that.
Go to Settings → Shortcuts on your iPhone
Note: If the "Allow Untrusted Shortcuts" switch is disabled, you need to open the Shortcuts app one time, click any Shortcut, and then close it.