What does it mean to switch a repository with a key?

Question

linux

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10

This command switches the repository, so I was told
As a result, all downloaded packages ( apt-get ) of the new versions

1. Which repository am I switching to with this command?
   
2. Is this a well-known repository or someone's personal one, and I'm downloading who knows what?
   
3. What is this key?
   

Answer 1

You just added the key to the list of trusted ones, nothing was switched anywhere. This key is used to digitally sign MongoDB packages. In order for your package manager to know that the package was received intact and from the owner of the key, you need to add the key to yourself in the list of known ones that you trust.
Although yes, this does not prevent MongoDB developers from putting left packages in their repository and breaking something, but there is already a question of trust in the owner of the repository.
Usually, after the specified command, there is a command to directly add the repository, then update the list of known packages, taking into account new ones from the added repository, then either update the packages (if the repository just has newer versions of the existing ones), or install new ones that have appeared from the added repository.