First as information, using
Magento 2.3.5-p2 and an own developed theme and a few extension.
When I do edit a CMS block and change the view to non editor the additional buttons for Insert Widget and Insert Image appears. So far so good.
But unfortunately when pressing the Insert Widget Button it is not opening the Page where I can select a Widget, but an 404 error page occurs.
I found, that in my setup, the function
$this->getPluginConfigOptions('magentowidget', 'window_url') returns an empty string. Therefore the on-click call of the insert widget button is resulting in the 404 error page.
In a fresh
2.3.5-p2 installation, this call contains the url and therefore it is working.
The call of these functions does happen in magento/Framework/Data/Form/Element/Editor.php
For the Insert Image Button, there is another function
This function returns correct URL, as well with the hash etc.
I do not see any extension overriding this
Editor.php class and therefore, I have no idea why this happens.
Does somebody had a similar problem or maybe an idea why this function returns nothing?
Looking forward to hearing from you. Best regards, Chequille