When a valid address is entered/pasted in the "Pay To" field and it belongs to a loaded wallet then it could note that.
Had the idea after #12688.
Currently, if you enter an address that has a label it will auto-fill the label field which has a similar effect.
It doesn't work if it belongs to other loaded wallet.
Moved to the GUI repo: https://github.com/bitcoin-core/gui/issues/63.