Maybe turning off Cellular Data for a minute or two might help.
Another thing you can try is to reset your network settings:
Reset your Network Settings. Tap Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.
– If you can't connect to a cellular network or cellular data - Apple Support
Tap on "Mobile Data" and wait for some time, until the list of apps loads at the bottom of that page.
Have you already used WhatsApp on Cellular Data on your iPhone 7?
I think Apps only show up in this list after you already tried to used the app on cellular data.
And all these app you already used on your iPhone 7 on Cellular Data don't show up on the app list under Cellular Data section?
So to get sure:
In your Settings app under Mobile Data at the end of that page in the section that is titled "Use Cellular Data for:" you have only listed two apps: Wallet and Facetime? It is the section beneath "Cellular Data Usage".
And after doing this you have already used WhatsApp using Mobile Data?
They only show up in this list after you have done so.
Have you tried to turn off and turn on again Cellular Data in the WhatsApp settings?
It's in Settings>Cellular.
Maybe WhatsApp appears in that section after you used it using mobile data.
Nope, it has nothing to do with that
Having this problem for over 4 months, I don't think it has something to do with waiting
Are any apps showing up at the bottom of the page?
Only Facetime and Wallet, but for example I have for some apps the "using mobile data" turned on and for some I don't (I have them set up from when I had the option available for them)
I use WhatsApp on Cellular Data already and it is still not showing up, neither all the other apps I've used on Cellular Data.
I tried both of your suggestions before, none of them is working
Missing settings on my iPhone