WP-admin says Sorry, you are not allowed to access this page

Check if you you are admin or not.

Make sure your user rule has not been changed by some plugin, etc.

Try manually resetting your plugins (no Dashboard access required). If that resolves the issue, reactivate each one individually until you find the cause.

Side note to @amsterdon ,

Please do not jump into other topics. If the troubleshooting already posted made no difference for you, then, as per the Forum Welcome, please post your own topic. A lot more people will see your post, and that way you stand a good chance of getting the assistance you want. Despite any similarity in symptoms, your issue is likely to be completely different because of possible differences in physical servers, accounts, hosts, plugins, theme, configurations, etc. Thus one problem, on one setup is not indicative of the functionality and reliability of an application as a whole.

I’ll be archiving your post.