I have created an offline wallet on an old phone.
I can create an unsigned transaction with the corresponding watch-only wallet and show it as a qr-code so it can be read by the offline phone.
With the offline wallet I go to "send" and read the qr-code (the unsigned tx). Then I can see the unsigned tx on the offline phone (as an info) but i cannot sign it or do anything useful with it (despite showing it as a qr-code again)...
You have to use the load transaction option not the send option. I'm not familiar with electrum for android so all I can suggest is that you look for a load transaction option.