The transition of Chromium browser to a snap package was planned since 19.10 and was announced on Snapcraft Blog. As of now I'm not aware of any other package with which with such transition happened.
You can always refer to package details on Ubuntu Packages or the output of
apt show package and check if it's dummy package and depends on snap. For example, in case of Chromium browser, package details mentions:
Transitional package - chromium-browser -> chromium snap
The output of
apt show also mentions that it is a dummy package and can be safely removed.
$ apt show chromium-browser
Maintainer: Ubuntu Developers
Installed-Size: 164 kB
Provides: gnome-www-browser, www-browser, x-www-browser
Pre-Depends: debconf, snapd
Depends: debconf (>= 0.5) | debconf-2.0
Download-Size: 48.4 kB
APT-Sources: http://archive.ubuntu.com/ubuntu focal-updates/universe amd64 Packages
Description: Transitional package - chromium-browser -> chromium snap
This is a transitional dummy package. It can safely be removed.
chromium-browser is now replaced by the chromium snap.