If you wish to use www, you should be adding an @ record along with it as well.

Also, have you tried removing and readding your app record?

Thanks! Yes, the 'www.' works fine, it's a marketing webpage and it would not accept an @ record. The application is the one using app record, and yes i've tried removing and re-adding twice now.

Some DNS providers do not support CNAME flattening (using a CNAME record on root domain). In that case, I would suggest migrating to Cloudflare’s DNS service.

https://developers.cloudflare.com/dns/zone-setups/full-setup/

I'm not trying to use the root domain. I apologize, I caused confusion by adding that in my original issue.
They're actually both working but one has SSL (the root/www) and the other (app record) does not. I'm suppose to have two SSL certs on my tier so that's why I started to seek support.

The root is fine, everything is working as expected.
The app record propagated but is not secure like it should be.

Have you tried accessing the site from an incognito browser or a different device? You might be encountering caching issues as I’m able to access it just fine securely.

That's great news! I feel so silly - that did end up working for me. Thanks so much!