TYPO3 Core

Moved to right project.
Guessed TYPO3 Version.

Which behavior would you expect?
a) just not showing the error message
b) rendering a proper preview of that dwg file as well

It seems, that dwg is not supported by ImageMagick (convert -list format).
In case my observation is correct, adding the mime-type to ImageMagickFile would just be a work-around, since that type cannot be processed by ImageMagic.

I'd suggest to avoid processing those files, in case they cannot be processed by ImageMagick at all. The file abstraction layer just considers any mime-type starting with image/ as image - however does not know about types that can be handled with ImageMagick - the (wrong) assumption is "ImageMagick can process all image formats":

https://github.com/TYPO3/typo3/blob/c02699a50f1ad7d4042c951f28eef28f43eb3577/typo3/sysext/core/Classes/Resource/AbstractFile.php#L308-L310

So, either there could be an exclude list to deny image/vnd.dwg (and other unsupported formats), or the capabilities and supported file formats of ImageMagick are auto-discovered by TYPO3.

A quick solution would be trigger preview rendering only, if the file extensions is configured accordingly in $GLOBALS['TYPO3_CONF_VARS']['GFX']['imagefile_ext']. Thus, prefer using AbstractFile::isImage() instead of AbstractFile::getType() === AbstractFile::FILETYPE_IMAGE like currently in the example below.

https://github.com/TYPO3/typo3/blob/d3f6c5f039fa7b4ad6544104bdc73db2b6d74db1/typo3/sysext/core/Classes/Resource/Processing/LocalPreviewHelper.php#L130

I was not able to reproduce this in the fileadmin/ file-list module (see screenshot below).
Can you please describe how you produced this in your environment? Thanks in advance!

(the test DWG file has been taken from https://knowledge.autodesk.com/support/autocad/downloads/caas/downloads/content/autocad-sample-files.html)

I think the problem can be solved with the suggestions of my previous comment.
Thus, I'd like to close this ticket. Please report back, in case something should be changed code-wise. Thanks!

Closing this ticket. Please reopen or create a new issue in case there are new aspects to this topic. Thanks in advance!