I have contacted them, and they replied me with this

Lucas (Slack) Nov 20, 9:15 PM PST

Hi there,

Thank you for taking the time to write in and provide this feedback. I apologize for the disruption to your existing workflows. Our aim is to build an editor that works for all Slack users to better format their messages and clearly communicate in channels, regardless of their technical expertise. While we are taking all feedback on board, disabling the new formatting tool isn't an option that we will be offering.

We are committed to doing what we can to improve the new experience for you, and will continue to make improvements to the new editor. If there are any specific examples of how these changes are impacting your daily work, please let me know. The more detail you can share about your experience, the better we can understand how to keep making it better.

Regards,

Lucas.

Anyone know how to reverse engineer Slack desktop client?

I've been using wee_slack.py for some time; if you can add an application token and prefer the weechat UI then it's an appreciable option, but the issues I've had regarding inputting code are not necessarily fixed there since weechat doesn't take multi-line input. :(

Link to wee-slack: https://github.com/wee-slack/wee-slack