I'm not wrong, the android version of Electrum lacks a lot of features that is present in the desktop version, coin control and fee customization is available on the desktop version of Electrum, but not on mobile and you can confirm that yourself if you use Electrum on mobile.
I agree that kind of messed up with the freezing address as coin control but I am sure that you can customize your fee in Android Electrum.
Also, it seems that now sign-in message is also available now but I am not aware of it or can't find it in my updated android too so probably it's still not updated on Play Store but the sign-in feature on the electrum android has been implemented recently.
No, it has not been implemented, you cannot sign a message in the android version of Electrum, you can only do that on desktop.
I saw that the request was marked as closed and since I was on my mobile I wasn't able to grasp the entire thread but now I see that it just led to another request which opened for the same request.