I believe Discord is quite prolific for surveillance and data mining,

Discord does not take any information from your PC other than what you input directly into the app. There has been confusion in the past because it's game detection would scan your file system for known games, but it wouldn't send that data anywhere and was only using it to detect when you were playing a game in order to update your status. As far as surveillance goes, I've not seen any evidence that they make profiles of individual users to sell to advertising firms, but I do believe that they track general trends inside of public community servers and use that information for something. They also integrate with a lot of 3rd parties such as OpenAI which may be doing something with the data they're given. They do seem to genuinely delete messages if they are deleted, which is a plus.