You can provide feedback to Apple here. I’d suggest something not too pointed but you do as you need.
yes Apple has an AppleTV app and an AppleTV+ app (and for added naming convention fun, AppleTV the streaming box). The AppleTV app is what you seem to be looking for(an App that allows to sync to various other channels/streaming services as well as to watch AppleTV+ and iTunes/Apple movie purchases library etc). What you have is AppleTV+.
As someone else mentioned — and with all due respect — this is your issue. If you want the AppleTV app available within your smartTV, you need to buy a Smart TV that offers it. It took a minute web search to see that AppleTV+ on Panasonic just started being offered 5 months ago. Apple is new to the Panasonic TV ecosystem. While the AppleTV app may come to it, or may not, it hasn’t yet. That is the limitation of the product you purchased.
Imho the best way is to opt for a streaming device, it doesn’t have to be an AppleTV box. A streaming box is where you’ll get the most app options with better and longer updates that have better UIs (and usability IME).