Front azure traffic from F5 LTM onpremises

The answer is yes technically you could do it.

You could have a site to site vpn between onprem and azure, receive traffic onprem and forward it to azure. Or even over internet having an ACL on azure to accept only your IPs

But the real question is why you need both an Azure application gateway and a 3rd party WAF?
And of course why protect a cloud app with onprem WAF?

Kindly provide more information about his to understand the requirement fully.