Hi Presind
You have migrated to a newer version of Apple Mail and the layout and options have to be configured to suit your requirements.
The Bin under "On my Mac" is the destination for mail that you delete from local mail folders, that is, previously read mail that you moved from mail inboxes the past and are are storing in dedicated folders locally.
To see your regular Bin(s) associated with your "live" email accounts you need to add them to the "Favourites" view.
At the top of the left-side-menu pane in Apple Mail hover the mouse cursor over the "Favourites" heading and after a short delay a round circle with a "+" sign will appear, alongside the "v" symbol.
Click the "+" circle and from the pop-up "Add Favourite" window select from the drop-down menu to add a Bin for a single Bin to catch deleted mail from all of your live email accounts then if desired scroll down to the individual configured email accounts and add a Bin for each account if your want to separate trash according to account.
While you are in that Favourites menu you can also add Bins for Junk Mail, and anything else that you want to appear under the Favourites heading.
Once configured you click on the "v" symbol next to the Favourites header to Show/Hide the contents of your Favourites listing.
For further help with Mail use the built-in help menu where this subject, and many others, are covered in greater depth and explained much more eloquently that I can write in this reply, simply click on "Help" > "Mail Help" from the menu bar at the top of the desktop view when Mail is open and is the actively selected application.
You will often find that the built-in help feature for all included Apple applications with macOS is a much faster and more convenient resource than using the forum to answer questions such as these as all we are doing is repeating what is already available in that help utility with your new Mac.
HTH
Will.
