The AMP project from Google might be killed off in the future. Currently, the official AMP plugin does not have an uninstall option or a UI to remove posts and options that the plugin will store in the site’s database.
The option to search for in phpMyAdmin would be using the following option name;
Then once the AMP option has been found you select and then delete it.
To delete the posts that the AMP plugin had created then the recommendation would be to use a plugin such as Bulk Delete in order to be able to achieve that.
Bulk Delete > Bulk Delete Posts
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The post type to search for would be named amp_validated_url then you can set all of those posts to be deleted on your site.
Bulk Delete > Bulk Delete Terms
The terms to delete related to the AMP plugin would be named amp_validation_errors.
If using the AMP for WordPress plugin then you can follow this help article to remove all AMP-related data from your site’s database. To enable the uninstall data option for the AMP for WordPress plugin go to;
AMP > Settings > Advanced Settings
All of the steps that are covered will help to be able to easily remove all of the AMP plugin-related data on your site and keep your site’s database free of bloat.