EDIT: My diagnosis was wrong, read the first comment

Hey. For a long time I was trying to find out why apps like GrapheneOS Info, Google Maps, Aurora Store, GitHub Mobile, and sometimes FCM (other apps were completely fine) had no internet access only on my home WiFi network. Actually, they thought they had internet access (otherwise I would get a popup explicitly stating that I'm offline), but just couldn't make connections (resulting in errors). I could, without any problem, make a request to the same domain or IP address shown in the error log in Vanadium or Termux.

Here is a sample error from the GOS Info app logs:

08-07 08:22:05.657 24218 24251 E ReleasesViewModel: Socket Timeout Exception
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: java.net.SocketTimeoutException: failed to connect to grapheneos.org/87.249.129.100 (port 443) from /192.168.1.107 (port 47058) after 10000ms
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at libcore.io.IoBridge.connectErrno(IoBridge.java:235)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at libcore.io.IoBridge.connect(IoBridge.java:179)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:142)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:390)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:230)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:212)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:436)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at java.net.Socket.connect(Socket.java:646)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.Platform.connectSocket(Platform.java:182)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.io.RealConnection.connectSocket(RealConnection.java:145)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.io.RealConnection.connect(RealConnection.java:116)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.http.StreamAllocation.findConnection(StreamAllocation.java:186)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.http.StreamAllocation.findHealthyConnection(StreamAllocation.java:128)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.http.StreamAllocation.newStream(StreamAllocation.java:97)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:289)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:232)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:465)
08-07 08:22:05.657 24218 24251 E ReleasesViewModel: 	at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:411)
(and the stacktrace goes on...)

I just found out that the fix to all of this was to go into my WiFi profile's settings and change Network usage from Detect automatically to Treat as unmetered.

My question is:

How does Android detect if a WiFi network is metered and why did it detect my home network as such? (no other Android devices [not running GOS] on my network ever had this problem, and this problem also disappears when connecting to a different WiFi network)
Why does a metered WiFi connection straight up remove internet access for some (seemingly randomly chosen, but always the same) apps? Shouldn't it just reduce background network usage and tell app store/sync service apps to not perform their work unless the user explicitly requests an update/sync?
Why does switching to mobile data immediately resolve the issue, if should also be considered a metered network (or is it only considered so when roaming or with data saver enabled)?