Maybe you should explain how you use the PHP part of the editor.
I think you fix an issue with changes in the Javascript where the problem is created in the PHP plugin.
For a quick fix I edited the core code (4.0) yesterday to make it possible to set a custom (form field) height. I think those parameters are removed in 4.0 but they are still used in the code.
You're fine with a width of 100%. Set a div container around the editor if you need to control the width.
If you need to control the height, you have to explicitly set a height. And that seems not to be possible.

sorry, this is a wrong fix,
you have to use TinyMCE width/height options, instead of hacking around

@Fedik
You are right but there is and was a problem in the tinyMCE plugin. line 366 and following in J4.0

 $html_height = $this->params->get('html_height', '550');
 $html_width  = $this->params->get('html_width', '');

You can't find those params in 4.0 i understand- thank God - but used in the code.

Used in line 595, 596

 'height'             => $html_height,
 'width'              => $html_width,

When I change this to use $width and $height, it works as expected for me.
You can skip the width as tinyMCE sets a default to 100%. This leaves it to the Html to set a div container around the editor if needed. The height has to be set if you want to restrict it. The height is the height of the editor including the toolbar and buttons used internally by tinyMCE. You can still resize the area if option is set.
I so far use a plugin to override this behavior as needed.

Please check this.

@schnuti , i have another PR, i believe it probably fixes your issue as well. see #26755

sorry, this is a wrong fix,
you have to use TinyMCE width/height options, instead of hacking around

Those options cannot be used for dynamically created editors.

Those options cannot be used for dynamically created editors.

what do you mean with "dynamically created editors" ?
you should show full example of your code

Those options cannot be used for dynamically created editors.

what do you mean with "dynamically created editors" ?
you should show full example of your code

I meant if the editor is created via javascript.

@DerinMavi
You can instantiate tinyMCE with Javascript without using Joomla PHP-methods. I do that for inline editing in frontend. Set your own selector and any options you need.

I meant if the editor is created via javascript

That not an answer, but if you instantiate tinyMCE with your own JavaScript then how it related to JoomlaTinyMCE.setupEditors?
as @schnuti already wrote, in your own code you free to do anything

That not an answer, but if you instantiate tinyMCE with your own JavaScript then how it related to JoomlaTinyMCE.setupEditors?
as @schnuti already wrote, in your own code you free to do anything

Yes, but I can't. JoomlaTinyMCE.setupEditors() is attached to DOMContentLoaded. After that event triggers; it replaces all textarea's with TinyMCE's, and because it has no prior knowledge of dynamically created textarea's - it uses default settings to configure TinyMCE; overwriting inline attributes of textarea elements. Inline attributes should be #1 in order of precedence.

@DerinMavi
And what happens when you change the selector in your example "js-editor-tinymce" to "my-editor-tinymce"? Still touched by Joomla? Then this should be wrong.

As far as I can see it not Joomla! issue (you did not provide any code that can prove opposite)

@Fedik yes, I think we can close this