This has been caused by #46438 removing the default height and with in libraries\src\Form\Field\EditorField.php

I think we need to add default width in to None editor.

Kind of:

if (!$width && !$col) {
  $width = 100%;
}

@Fedik as shown in the screenshot it is a problem with BOTH editor none and editor html - thats why I went to the time to specifically include both in my screenshot. The same problem of setting height and width with empty values also exists if the global editor is set to codemirror its just not as obvious as the width is set again inside codemirror

Did you made clean installation or?
Can you please check TinyMCE config, it have 700px width in the plugin parameters? I suspect that the case.

if not, then need to debug more :)

stop guessing

Do you have or not the width in the plugin configuration?

lesson learned - wont waste my time any more. thanks and bye.

Man, I asked you to do a simple thing.

Please check the TinnyMCE plugin, width parameter.
On old installs it was 750px, and it may explain your finding.
On new install it should be 100% after #46438

We do not update this parameters during upgrade.

i've moved on - not wasting my time in reporting bugs with detailed explanation of the change that caused it ever again you clearly have no interest in anything but victim blaming

Nto just mail templates - the same problem exists on front end editing