Quote from: Joe-Bloggs on March 12, 2024, 07:38:46 PM

-snip- I don't know who is correct and I can find no mention of importing an electrum watch only wallet generated psbt file into a bitcoin core wallet.

It's easy to test this with "TestNet" since Electrum wont have to sync the test blockchain to do that and Bitcoin Core will remain offline in your use-case.

To start Electrum in testnet, you either start it using with the command line argument --testnet
or (exclusively in) Windows, create a shortcut and add --testnet after "Target" in the shortcut's 'Properties'.
You can get free test coins in various testnet faucets.

Take note that you must finalize the (fully signed) PSBT in Bitcoin Core using finalizepsbt command for it to be converted into raw transaction that's compatible with other broadcasting tool/sites/wallets.
If to another online Bitcoin Core, the fully signed PSBT in the GUI will work.

Quote from: Joe-Bloggs on March 12, 2024, 07:38:46 PM

Is it possible to create a watch only wallet in electrum . Feed in the public address of a bitcoin core cold wallet.
Create a psbt with the electrum watch only wallet and save to file. Then where it says load psbt file in bitcoin core v21 just load in that electrum generated file?

As i've said in the other thread, yes:

Here's a demonstration:
(I've used regtest Bitcoin Core and Testnet Electrum so the bech32 address' format is different but keys and transactions are compatible)

In watch only Electrum that contains an address from Bitcoin Core, create a transaction and export it as file.

Load the psbt file to Bitcoin Core, Sign it and Export it using "Save..." or "Copy to Clipboard".

Load the signed PSBT file to Electrum and you should be able to broadcast it.

But as my note above implies, some script types may require you to finalize it first using the said command.