We are using Sitecore 9.1 and SXA. When we try to open any page in the Experience Editor, Publish button is not getting displayed under the Home tab. This is not happening over all the environments.
To mitigate this quickly you can create the Package for the below item from the working environment and publish it back to the instance where it has a problem.
This might solve your issue quickly and later you can compare what was the difference.
Check if you have below item configured correctly in your stripe
Check if the page you are trying to publish is under any custom workflow which has this rule as part of workflow.
Solution 4: Raise ticket to Sitecore Support.