If you select your account, there's an option to "Export" the account in xPub format. That's the same as sharing a public address. Anyone with an xPub key can import it as watch-only and see all your addresses and balances, but can't spend from it.
Hm, so could you now or in the future...
import your Mycelium xPub to Electrum, then use Mycelium to sign unsigned TXs generated by Electrum?
OR
import your Mycelium xPriv to Electrum, delete the xPriv out of Mycelium, leaving only the xPub, then use Electrum to sign unsigned TXs generated by Mycelium?