Color markings for .log files, not for .txt files

Describe the bug
Allright guys, I'm at a loss. I've spend the better part of today trying things, but I'm not getting this done. My problem is that Text opens my .log files correctly, but with colored text and also parts are italic. It recognizes the .log files as plain text correctly, because I have added the log file type as text/plain to mimetypemapping.json. So no rich editing, like it's supposed to do. But it appears to be formatting the text in some way anyway. The .log files are essentially just text files, but with a .log extension. If I change the extension in Nextcloud to .txt, the file loads correctly as plain black text without any formatting.
Edit: FYI: the log files in question have nothing to do with Nextcloud or Text, they are just log files for things I'm running on a server.

To Reproduce
Steps to reproduce the behavior:

1. Open file with .log extension.
2. See parts of text are colored, and some text in italic and maybe some other formatting.
3. Close file, and change extension to .txt.
4. Open file again, and behold! A plain text file without any formatting.

Expected behavior
Any file type that has been added as [text/plain] should be shown just like that: as plain text. (right?)

Screenshots
File with .log extension

Same file but now with .txt extension

Server details:

• Nextcloud version: 28.0.1
• PHP Version: 8.2.13
• Database: Mysql 8.2.0

Client details:

• OS: Windows, Linux
• Browser: Chrome
• Browser version: 120.0.6099.217
• Device: Laptop, phone, desktop

Nextcloud log (data/nextcloud.log)

Nothing is showing in the logs

Browser log

I'll add this when needed.

Start by reproducing the behavior with a .log file configured as text/plain in mimetypemapping.json, then compare it with the same content saved as .txt. Trace how the editor chooses formatting for these extensions. Done means text/plain files display as unformatted plain text regardless of whether the extension is .log or .txt.