-snip-
both are same version 4.2.0
Then it should work without any issue.
The video you linked is too old but the steps should be similar.
Basically, you need to create the transaction in the watching only wallet, then export it using "
Export->Export to file".
Then transfer the .psbt file to the offline PC; Open cold-storage Electrum and use "
Tools->Load transaction from file" then browse to the .psbt file's directory.
Load it, click "
Sign" (
type your password),
then export the signed transaction to the online PC (
same menus as the first step).
load the signed transaction to the watching only Electrum (
same menus as the second step)
Review the transation's details and click "
Broadcast" to send it.
If you're thinking of "
updating" the balance of the offline Electrum, then it's unnecessary since bitcoins aren't stored in Bitcoin wallets.
It's
locked in the blockchain which is in every full node of the Bitcoin network, wallets do not receive bitcoins but only "
watch" coins that they can spend.
Your offline Electrum has the necessary
key to spend it while your watching-only wallet watches for the balance.