I already failed at step 5 "open a transaction via "Right-Click->Details" -> I can only click on details in the addresses tab, where I clearly see the ones with still spendable-outputs available. However nowhere I can find a "Share-> Copy to Clipboard" option.
I found something similar though in the Coins tab. If I click on Details there is an "Export -> Copy to Clipboard" option. I tried that and then import via mSIGNA via Transactions->Import Transaction->From Clipboard (raw). It crashed the wallet. lol (no worries I backed it up before).


EDIT: BIG UPDATE! It worked! I hadn't unlocked my keychain when I first tried to import and mSIGNA crashed. However I just tried again and it actually worked. Importing to mSIGNA, then, with finally a correct sync state I was able to select the right spendable outputs (actually just the address holding the coins) and then sign the transaction, import to electrum and broadcast there.