David, have you considered such a case that someone just wants to browse the forum and does not want to accept cookies? The extension does not allow you to opt out of cookies and to use the site passively - without logging in. A significant part of the traffic, and perhaps more comes from readers who do not have an account on the forum, but only want to read. phpBB works properly without logging in without using cookies. When someone has blocked cookies in your browser and visits a forum with your extension, they will not be able to view it even if they click [accept]. Try to block cookies in your browser and enter the forum provided in the previous post https://allabouthd500x.altervista.org
Of course you can leave it this way, but maybe there is some way to block phpBB cookies by adding the [do not accept] button.
I am currently looking for the right solution in Joomla because they have not yet prepared a new version compatible with GDPR. I found a plugin that blocks Joomla's own and external cookies using PHP Reflection. I do not know what PHP Reflection is, maybe it's useful for that.
In addition, this plugin records every consent to cookies in a separate table (IP, time, accept). Maybe it is unnecessary but we probably need to register these consents.