Many thanks for sharing, very useful indeed. From reviewing your Site Health information the site status appears as “none”, and from the screenshot you kindly shared this depicts a “Invalid site state null” error.
While this error may be due to a slow communication between your site and AdSense servers, in order to obtain your site status, another possibility is a slow network. This is based on the console errors in the screenshot you shared.
In order to try and complete AdSense set up within Site Kit please follow the steps below. These steps help rule out any third party plugin conflicts, some of which may be making network request:
- Login to your site from a Chrome browser incognito window
- Install and activate the Health Check & Troubleshooting plugin.
- Navigate to “Plugins > Health Check & Troubleshooting > Troubleshoot”.
- From the same screen click on the “Available Plugins” tab at the top right and then click on the “Enable” option next to “Site Kit by Google”
- Attempt to connect the AdSense module once more
Let me know how you get on with the above. if the same error appears please any warnings or errors when checking your Site Health status (Tools > Site Health > Status), which differs from your Site Health information requested above. Such errors may include REST endpoint references.