@Asifahmed have you checked to see if there is an AutoPkg recipe to create a .pkg installer for the application? If not you can manually create a package for it with Composer as you describe, or you can use this tool to create a .pkg from the .app: https://github.com/scriptingosx/quickpkg

Which app is this? The developer may have an enterprise download available that you can get in pkg form. Also, you could check the list of apps that Installomator installs. https://github.com/Installomator/Installomator/blob/main/Labels.txt

Using Installomator is very easy. Once you have the script attached to your install policy, you just use parameter 4 to fill in the label corresponding to the app you want to install.

It completely depends on the .app. Is the .app the actual application or is it an installer for the application. In general, if the .app is the application itself then you should create a pkg to distribute it. The purpose of a pkg is to copy files to a specific location and possibly run some scripts before and after then copy. 

As others have said, you may want to check for a enterprise version installer. A lot of the time this is basically just the app wrapped in a pkg. Zoom and Chrome both provide installers such as these. 

Copy the .app file to /Applications/ then run 'pkgbuild' before uploading to your distribution point;

pkgbuild --install-location /Applications --component /Applications/MyApp.app ~/Desktop/MyApp.pkg

for DMGs or downloads that are just an .app I use this:

https://github.com/rtrouton/Simple-Package-Creator/

allows you to add metadata for pkg receipt and version number.. which in turn you can then see and scope for.

Nice, i'd never come across that tool.
Looks like it uses pkgbuild cli as part of it's tools and likely how it adds version numbering, identifier etc. as well.

note that after you give it the app it shows the wrong dialog about adding an app again.. but it works..