What I'm trying to tell you is to do it without the iframe first.
In other words you ought to just be able to take the full URL from the canvas work pad after you've done the anonymous login.
Copy that full URL, put in the anonymous hint in the proper place, paste it in the address bar of a new incognito browser and it should take you directly to the dashboard without the login page.
You need to get that to work first, if that does not work the iframe will never work.
The iframe just adds an extra complexity get this to work first.
Awesome! but unfortunately I'm not an iframe expert so perhaps what you should do is open a new thread with subject like "anonymous access works but iframe for canvas doesn't" perhaps you'll get some help from front end people.
Alright! I was able to run through all the steps on a Cloud instance running 7.11.2. I Was able to get this working no problem in Firefox but it looks like Chrome and Safari are a bit more strict with the iframe.
The fix is to set xpack.security.sameSiteCookies: None in the kibana.yml. Once I did that, I was able to access the Canvas workpad in Safari and Chrome. You can read more about this setting here: Security settings in Kibana | Kibana Guide [7.13] | Elastic
Also, I'm def going to update my original post with this info
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