[2021] Is it any way to reset a chunk? I made a mistake and now a huge chunk is leveld

No, you cannot reset chunks. You could either restore a backup or fill the chunk up again, but that will cause it to only consist of the material you have specified with the level command.

Any commands should always only be used when you know what you do, insofar we do not plan to implement any warnings, unfortunately. The wiki is showing what each command does and we always recommend to get used to commands on a test world first. Pretty much every single command when used wrongly can be dangerous, so it's absolute necessity to learn how they work before using them in production, no warning can offset that.

Commands at this point in development are also not a development goal, their current use is mostly for QA and many of them are still QA only commands that can onyl be used by players that own Developer Tier. Later on in the development process we'll surely take a look on making commands more straightforward and easy to use, but they will still always be stuff you need to know what you are doing - that's why they are only for admins.