Create unsigned tx (PSBT) in a watch-only wallet using bitcoin core, sign it in electrum and broadcast using bitcoin core What are the steps that we can follow to create an unsigned tx for watch-only cold storage address using bitcoin core? How can we sign the transaction and broadcast it later?
Run the below commands in electrum console:


>> getaddresshistory('tb1qu2l4n8st9w3hhsxstd8muaxgnu63fql9rkylmd')
[
    {
        "height": 1807710,
        "tx_hash": "727707cced87f9bc2a1ca3ed28df39588e9881fd50c272e78bc76a5bb1ffde9c"
    }
]
>> deserialize(gettransaction('727707cced87f9bc2a1ca3ed28df39588e9881fd50c272e78bc76a5bb1ffde9c'))
{
    "inputs": [
        {
            "coinbase": false,
            "nsequence": 4294967295,
            "prevout_hash": "99ebe2d047c545a50cf86f0ff5f4c0648437cb8724137f1a33c2f06eb06ef35a",
            "prevout_n": 1,
            "scriptSig": "",
            "witness": "0247304402206379d344d75fbee07f54213378f95e44dc757872d59a35efbc14ec7e1ca7dfd102207a47f9c1be39cafa8f9ac8a879e2b968e2359bead23a1f6598478ed7d141c73d012103ee169045615c663c0204472f86e3c2b2ae43e574146d30607c42fe6d670ac7be"
        }
    ],
    "locktime": 0,
    "outputs": [
        {
            "address": "tb1qu2l4n8st9w3hhsxstd8muaxgnu63fql9rkylmd",
            "scriptpubkey": "0014e2bf599e0b2ba37bc0d05b4fbe74c89f351483e5",
            "value_sats": 3000000
        },
        {
            "address": "tb1q7sx47sra5w7kw8we5xeusl4089ryverhjcft6q",
            "scriptpubkey": "0014f40d5f407da3bd671dd9a1b3c87eaf3946466477",
            "value_sats": 61797954
        }
    ],
    "version": 2
}

You get the scriptPubKey in above output which can be used in importmulti command in bitcoin core:
"address": "tb1qu2l4n8st9w3hhsxstd8muaxgnu63fql9rkylmd",
"scriptpubkey": "0014e2bf599e0b2ba37bc0d05b4fbe74c89f351483e5"
Get the public key of the address from details:

If you are using bitcoin core wallet instead of electrum in this example, you can run the getaddressinfo command in console to get scriptPubKey and pubkey of the address.
Run the below command in bitcoin core console to import the address with the details copied from electrum:
importmulti '[{"scriptPubKey" : "0014e2bf599e0b2ba37bc0d05b4fbe74c89f351483e5","pubkeys" : ["0304c5184085eea27a072628de03fbb953f5fdd99fb526f097fdd4c6968d165f1a"],"timestamp" : "now","label" : "watch-address-test", "watchonly": true}
You can ignore the steps mentioned above for scriptPubKey and only use the &quot;Public Key&quot; of an address by using descriptor:
We need checksum in importmulti which is returned in descriptorinfo for the public key mentioned

Next, we can run importmulti command (I have used public key for a different address in this command):

importmulti '[{"desc" : "wpkh(026641b79d7ffa40ddf994f0277c2649f3ddcbd871194ba6ef87687daea22ca503)#zl4yt8hu","timestamp" : "now","label" : "watch-address-test", "watchonly": true}]'


rescanblockchain 1800000 1835099
I can see available inputs in GUI:

We still get an error if trying to create an unsigned tx which involves sending some amount to change address because we aren't trying to spend the whole balance.

Add a change address for creating unsigned tx:

Option to copy PSBT:

Load transaction using the copied text in electrum:


Copy the hex of signed tx and run the below command in bitcoin core:


sendrawtransaction 020000000001019cdeffb15b6ac78be772c250fd81988e5839df28eda31c2abcf987edcc0777720000000000fdffffff02b3410f0000000000160014112c8ecb9e0876a645e7b8e89eed83bd61096e2c80841e00000000001600145f24e8fbfe65840c27dad3b053855de4cee843820247304402200d7cc29a8588c180e6a460e0eb88ea830db76dbb040a875d45fe8c64c9509a80022060879365af1c6d19e7c47bdbfa402a053ed42809c52db6816cd249dff46529b001210304c5184085eea27a072628de03fbb953f5fdd99fb526f097fdd4c6968d165f1a5f001c00


It returns the transaction id: 4890c14e7635a3e72320046645686052339e443eba56e5a62849a48b3f67f419
You can check the details in a block explorer: https://blockstream.info/testnet/tx/4890c14e7635a3e72320046645686052339e443eba56e5a62849a48b3f67f419
Related questions:
How to create unsigned tx in a watch-only wallet?
How to move/sweep your Bitcoin Core bitcoins safely and air-gapped to your new fancy cold storage?
Related issues:
https://github.com/bitcoin-core/gui/issues/94