There isn’t a way to automatically do these things since it’s important that folks know the URL of the site they’re visiting. This is important for security of the web.
But if you want to actually create an app and distribute it, I recommend looking into Phonegap Build: https://build.phonegap.com/. There might be better solutions than that which other forums members can recommend, but that seems like a powerful tool for building what you’re hoping to do.
1 (easier): Create a service worker. Look for it on the internet. You can create a basic servie worker. Once Chrome detects it, it gives users an option to add the app to the homescreen. What it does is, it places your favicon in the app drawer o the Android phone and thus, it feels like a native app. It doesn’t show the URL, etc. Might get your work done. However, it can’t really be customised much. On the other hand, you don’t just get an Android app, you get an app that can be installed on all operating systems on which Chrome runs. Bonus: You can use this great tool from Microsoft: https://preview.pwabuilder.com/ (Not tried by myself).
2 (difficult): You can use Android Studio to make an app. Look for WebView implementation in Android. I had made once, I can share the source code, but, it’s useful only if you know Java. However, it’s a completely native Android app and thus, you can customise it the way you want.
3 (easy, not recommended): There are services like AppYet, etc., which can let you created an Android app with the URL of the website, but, it includes a lot of unwanted code and thus, the generated APK size is like 10MB (whereas, the one I made myself summed up in 2MB). There are a lot of unwanted and not-needed elements in such apps. Also, it’s not really very customisable. But, it can get the job done.
Yeah, sure, I’d love to. However, this would take some time. My laptop is busy rendering a 3D animation and then, I have to test if the app works fine with all the latest Android SDKs. Consider a day or two for al this.
That’s an interesting idea, probably something interesting to take up in these lockdown days. However, I do not have a great experice in creating and managing a GitHub repo. Also it’s now ages since I las touched Android Studio. So, this might take some time. If someone else can come up with one till then, that’d be great, or, I’ll do it as soon as possible.
This seems like a great starting point for Android development, though it doesn’t have Firebase integration. It was updated just a couple days ago. And it provides information on how to structure the app for either local HTML files, or loading from a remote URL: