Steps to reproduce on regtest:

```
converttopsbt 02000000000101ab73dba46508bacdb49a988ddd74bc9d39c9cb7e057af060ca8c6b6861e28e3c0300000000feffffff02b828d0b20000000017a914d1954862afd728fbb055149002958e1d1b9e1f0b8700ca9a3b0000000017a91442170ccb3441cff1723af9afab6f2553103e1d578702473044022077380c6e16496d9905aef120694c329be51522847cb5d53fa74b94698c95678d02202d32c46e0e17420a83dee830fefda7d40529182f5d82be47c2b49a7b83214ab50121026d483d6628dcc3ef6e3ab9ed4937c452c263c7e0ac80eb4be97426d5da8f640500000000
```
or 
```
converttopsbt 02000000000101ab73dba46508bacdb49a988ddd74bc9d39c9cb7e057af060ca8c6b6861e28e3c0300000000feffffff02b828d0b20000000017a914d1954862afd728fbb055149002958e1d1b9e1f0b8700ca9a3b0000000017a91442170ccb3441cff1723af9afab6f2553103e1d578702473044022077380c6e16496d9905aef120694c329be51522847cb5d53fa74b94698c95678d02202d32c46e0e17420a83dee830fefda7d40529182f5d82be47c2b49a7b83214ab50121026d483d6628dcc3ef6e3ab9ed4937c452c263c7e0ac80eb4be97426d5da8f640500000000 false
```

Further reading: #13738
view.SetBackend(viewMempool); 
        for (const CTxIn& txin : psbtx.tx->vin) {
            view.AccessCoin(txin.prevout); 
        }
        view.SetBackend(viewDummy); 
    }
    
    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
        PSBTInput& input = psbtx.inputs.at(i);
        if (input.non_witness_utxo || !input.witness_utxo.IsNull()) {
            continue;
        }
        const Coin& coin = view.AccessCoin(psbtx.tx->vin[i].prevout);
        std::vector<std::vector<unsigned char>> solutions_data;
        txnouttype which_type = Solver(coin.out.scriptPubKey, solutions_data);
        if (which_type == TX_WITNESS_V0_SCRIPTHASH || which_type == TX_WITNESS_V0_KEYHASH || which_type == TX_WITNESS_UNKNOWN) {
            input.witness_utxo = coin.out;
        }
    }
    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
    ssTx << psbtx;
    return EncodeBase64((unsigned char*)ssTx.data(), ssTx.size());
}
UniValue joinpsbts(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() != 1) {
        throw std::runtime_error(
            RPCHelpMan{"joinpsbts",
            "\nJoins multiple distinct PSBTs with different inputs and outputs into one PSBT with inputs and outputs from all of the PSBTs\n"
            "No input in any of the PSBTs can be in more than one of the PSBTs.\n",