Comment 2 for bug 1958812

The format of the package is irrelevant for most end users, a warning wouldn't be helpful (quite possibly the opposite, it would make them think there is something wrong with the installation, when everything is working as intended).

Advanced users can use apt to read the description prior to installing:

    $ apt show chromium-browser | grep Description
    Description: Transitional package - chromium-browser -> chromium snap

And they always have the option to uninstall the snap afterwards if they really don't want it:

    $ snap remove chromium