Hi @Andrey Volkov, there is no setting to disable this function. You may submit a feature request in the Ideas Portal at https://support.ringcentral.com/new-case.html.

There's a way to find out deleted messages by exporting the chat logs. They are exported as a .zip file and inside it you have folder "posts" that contains a JSON file.
You can use a regular notepad to open it (I used Sublime text 4). Once you open it you see a lot of details. If you want to find out the deleted parts just search for the keyword "true" so they get highlighted. In the attached picture you can see I wrote "testing 3" and deleted it. You won't be able to know if people edit the messages Capture.PNG

here's also an article on how to export the logs
https://support.ringcentral.com/app/admin/desktop-web/requesting-message-data-exports-ringcentral-app.html