in TS3 I changed my chat font to a monospace font. Its very useful to send source code or compare it with others. But I cant find an option to change the font of the chat in the new client. Not even the font size. Is there any way to change the font?
In the new client you can simply send your code in markdown formatting and it will be rendered with a monospace font.
Put your code in between those backtick characters to send code blocks.
(This example contains zero width whitespaces to preserve formatting)
For more possibilities look at the markdown standard (Markdown Cheatsheet · adam-p/markdown-here Wiki (github.com)).
If you really want to change the font of the entire client you need to create your own custom theme. This is not an easy task, but you can look at my theme (github.com) for inspiration.