An additional piece of information that might help understand the issue: I have Phoca Download installed, and when attempting to create a new entry, the same error occurs.
URL: https://domain.com/administrator/index.php?option=com_phocadownload&view=phocadownloadfile&layout=edit

I disabled Phoca, including its components and plugins, but the error persists.

I have the exact same issue in several test installations. I'm not using Phoca Download, but I'm using YOOtheme Pro as a page builder. Maybe it's got something to do with that?

My system information is as follows:

System Information
Setting Value
PHP Built On Linux p-ri7cbt-2htxr-7f79f78bc8-7z89v 6.6.20-cloud-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.6.20-0gardenlinux0 (2024-03-06) x86_64
Database Type mysql
Database Version 8.0.36-28
Database Collation utf8mb4_general_ci
Database Connection Collation utf8mb4_0900_ai_ci
Database Connection Encryption None
Database Server Supports Connection Encryption Yes
PHP Version 8.2.24
Web Server Apache/2.4.59
WebServer to PHP Interface fpm-fcgi
Joomla! Version Joomla! 5.2.0 Stable [ Uthabiti ] 15-October-2024 16:00 GMT
Joomla Backward Compatibility Plugin Enabled ()
User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/129.0.0.0 Safari/537.36

I have the same problem under 5.2 and cannot edit existing articles either via the backend or the frontend. However, I have neither changed the standard image directory under Plugins System File System, nor do I have Phoca Download installed. The template is Helix Ultimate. This is very problematic, as I had no issues under 5.1.4. What additional information is needed? Here is the debug-info:

COM_MEDIA_ERROR_ACCOUNT_NOT_FOUND    
# | Function | Location
-- | -- | --
1 | () | JROOT/administrator/components/com_media/src/Provider/ProviderManager.php:128
2 | Joomla\Component\Media\Administrator\Provider\ProviderManager->getAdapter() | JROOT/administrator/components/com_media/src/Provider/ProviderManagerHelperTrait.php:97
3 | class@anonymous/www/htdocs/DOMAIN REMOVED/plugins/editors/tinymce/src/PluginTraits/DisplayTrait.php:333$15->getAdapter() | JROOT/administrator/components/com_media/src/Provider/ProviderManagerHelperTrait.php:151
4 | class@anonymous/www/htdocs/DOMAIN REMOVED/plugins/editors/tinymce/src/PluginTraits/DisplayTrait.php:333$15->getDefaultAdapterName() | JROOT/administrator/components/com_media/src/Provider/ProviderManagerHelperTrait.php:123
5 | class@anonymous/www/htdocs/DOMAIN REMOVED/plugins/editors/tinymce/src/PluginTraits/DisplayTrait.php:333$15->resolveAdapterAndPath() | JROOT/plugins/editors/tinymce/src/PluginTraits/DisplayTrait.php:338
6 | class@anonymous/www/htdocs/DOMAIN REMOVED/plugins/editors/tinymce/src/PluginTraits/DisplayTrait.php:333$15->prepareTinyMCEUploadPath() | JROOT/plugins/editors/tinymce/src/PluginTraits/DisplayTrait.php:352
7 | Joomla\Plugin\Editors\TinyMCE\Provider\TinyMCEProvider->display() | JROOT/libraries/src/Editor/Editor.php:211
8 | Joomla\CMS\Editor\Editor->display() | JROOT/libraries/src/Form/Field/EditorField.php:250
9 | Joomla\CMS\Form\Field\EditorField->getInput() | JROOT/libraries/src/Form/FormField.php:482
10 | Joomla\CMS\Form\FormField->__get() | JROOT/libraries/src/Form/Field/TextareaField.php:94
11 | Joomla\CMS\Form\Field\TextareaField->__get() | JROOT/libraries/src/Form/Field/EditorField.php:138
12 | Joomla\CMS\Form\Field\EditorField->__get() | JROOT/libraries/src/Form/Form.php:458
13 | Joomla\CMS\Form\Form->getInput() | JROOT/administrator/components/com_content/tmpl/article/edit.php:73
14 | include() | JROOT/libraries/src/MVC/View/HtmlView.php:416
15 | Joomla\CMS\MVC\View\HtmlView->loadTemplate() | JROOT/libraries/src/MVC/View/HtmlView.php:204
16 | Joomla\CMS\MVC\View\HtmlView->display() | JROOT/administrator/components/com_content/src/View/Article/HtmlView.php:135
17 | Joomla\Component\Content\Administrator\View\Article\HtmlView->display() | JROOT/libraries/src/MVC/Controller/BaseController.php:697
18 | Joomla\CMS\MVC\Controller\BaseController->display() | JROOT/administrator/components/com_content/src/Controller/DisplayController.php:65
19 | Joomla\Component\Content\Administrator\Controller\DisplayController->display() | JROOT/libraries/src/MVC/Controller/BaseController.php:730
20 | Joomla\CMS\MVC\Controller\BaseController->execute() | JROOT/libraries/src/Dispatcher/ComponentDispatcher.php:143
21 | Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch() | JROOT/libraries/src/Component/ComponentHelper.php:361
22 | Joomla\CMS\Component\ComponentHelper::renderComponent() | JROOT/libraries/src/Application/AdministratorApplication.php:150
23 | Joomla\CMS\Application\AdministratorApplication->dispatch() | JROOT/libraries/src/Application/AdministratorApplication.php:195
24 | Joomla\CMS\Application\AdministratorApplication->doExecute() | JROOT/libraries/src/Application/CMSApplication.php:306
25 | Joomla\CMS\Application\CMSApplication->execute() | JROOT/administrator/includes/app.php:58
26 | require_once() | JROOT/administrator/index.php:32

</div><!--EndFragment-->
</body>
</html>

This appears to be the result of the changes made in #43579

I can replicate the bug and if I revert the changes in that PR the bug is cleared.

Hope that helps someone to resolve the bug

Thanks Brian! :)

This appears to be the result of the changes made in #43579

Thank you, Brian, for the references provided in #43579.

In my case, the issue was related to TinyMCE. In the plugin, the "Images Directory" option was not defined. After setting it, the editor started loading correctly.

Plugins: Editor - TinyMCE

Please follow the comment #44277 (comment)
That should fix it for now.

I close this as duplicate of #44285

Please test #44313