Golden “Southsea Deckhand” cannot be used in standard mod.
It can be used in wild and twist modes, but not in standard mode.
“Shadowstep” and “Preparation” are available, but “Southsea Deckhand” is not available.
What do you mean “cannot be used”?
Do you mean that your collection simply does not HAVE a golden version of southsea deckhand?
This is a Core card for 2024, and golden versions of Core cards are unlocked with achievements. I assume that you just do not have the appropriate achievement to unlock this card.
I think that the card is available for wild/twist because those formats allow the Legacy version of the card, which you do own in golden.