When launching java app as Mac app there default java process name and About description instead of mine
If you use a shell script you must run it from a shell and so to ghet a shell macOS opens Terminal. You are also not running an app so not getting the correct setup for icons, menus etc.

To be seen as an app the executable needs to be packaged as per Apple's Bundle documentation

This Platypus seems to say it should do this. So in this case you need to read its documentation and see what you have not done. If this is the problem then this would need to be a question on StackOverflow but you would need to show how you set your app up.