The nlocktime parameter in createrawtransaction seems not work using Bitcoin Core Wallet GUI
You're putting the locktime in the wrong place. You have

"[{\"txid\":\"myid\",\"vout\":0}]" "{\"address\":0.01, \"address\":0.01} 20"


but it should really be

"[{\"txid\":\"myid\",\"vout\":0}]" "{\"address\":0.01, \"address\":0.01}" 20


The locktime is a separate parameter, not part of the quoted parameter that has the transaction outputs. It goes outside of those quotes.