People who only watch content on YouTube don’t need an account and won’t have a handle.
But if you want to keep a list of your favourite channels, want to be alerted when new content has been added to your favourites, want to create playlists and would like to be able to comment on content then you need an account. YouTube call this your channel.
If you have a channel, you will have been assigned a handle or will have chosen one. It will be @something.
To find it go to YouTube and and look for the You icon - it’s usually on the left hand side of the screen - a black box with a white arrow under Home, Shorts, Subscriptions. If you can’t see it make sure you have clicked the YouTube name at the top next to the red box with a white arrow in it. Alternatively you can click your channel icon, the circle top right.
Click You (or channel icon) to see your channel name and handle - so it might show say Florence Smith @auntieflo if that’s how you have set it up. If you have ever commented on content, it will display as a comment from @auntieflo not Florence Smith. It’s not really very different to how we choose user names here. As Baggs says, your handle on GN is Auntieflo.
This is what the message is about. YouTube now supports 75 languages. The company is planning to change handles to better reflect the user’s preferred language but they are giving the user the opportunity to leave their handle as it is. I don’t think English language users are going to be affected by this as that’s the default language but if, for example, Florence Smith has set her preferred language to French and makes comments in French they might try to change the handle to @tanteflo. YouTube are effectively asking users to set their handle now if they don’t want to be swept up in what could be a mass of automated handle changes probably using AI. Does that make sense?
If you did wanted to change your handle anyway - click your channel icon - the circle top right; view your channel; customize channel. You might see something different as there are different route to this and they all show something a little different. You are looking for an option that says basic info. You can change your handle there.
I hope that explains things.