Getting started - WAN Internet Connectivity Issues

[cookiemonster]

Ah Ok, that will help.
You've gone over the documentation for first setup, and have a DNS setup on OPN? We'll get to the ping question but in my opinion, getting the basics of setting up OPN will ensure there's nothing getting in the way of ping working for you.
So DNS setup and clients getting an IP address, and resolving names, appearing in DHCP leases?
Please confirm what are the DNS servers in general settings and dnsmasq/unbound if you are using any.

[cliffwilliams44]

What IP address is your OpnSense device getting from your ISP?

You say "public", but that's no always the case with modern ISPs.

If it is a 10.x.x.x, or 172.16.x.x or 192.168.x.x then this is a private IP address.

If so, under Interfaces -> [WAN] -> Generic configuration uncheck "Block private networks".

This is not a setting in psSense so if you are a previous pfSense user like me, this setting is a gotcha you are not expecting.

[cookiemonster]

I imagine you're talking about CGNAT. Fine, semantics are important. The OP stated he is pretty knowledgeable, so this is assumed known and understood.
That said, those are the known RFC1918 networks, they are always private and should NOT be allowed from the WAN side unless you really know what you're doing. There's a reason they're blocked by default on WAN in.
So back to the thread, the "public" ip in this context it the one assigned by your ISP.

[CursedGravity]

I followed this guide: https://homenetworkguy.com/how-to/beginners-guide-to-set-up-home-network-using-opnsense/.  That should tell you what my DNS settings are. 

[cookiemonster]

This linked guide is not the basic one, for instance it includes VLANs, that might be something you won't be using. Even if you wan to use them later, right now you just want to setup the basic system, right?
I suggest you use another of his guides https://homenetworkguy.com/how-to/install-and-configure-opnsense/
The more relevant part of it is the configuration after installation.

[CursedGravity]

I have gone through the wizard already. 

[cookiemonster]

Ok then. Now you have WAN and LAN setup. What is exactly the setup with services setup and how i.e. DCHP which version?, which pool, DNS is by what Unbound, something else?. What is exactly the problem, include details like ip addresses involved, any VLANs, switches involved, virtualisation, etc.
I'm not asking to describe everything, it is too much and many not needed to identify what the problem might be BUT one-liners don't help that much