Can Forge of the Future kill itself and target itself to return back to the deck?

No, Forge of the Future cannot recycle itself.

According to RiftJudge FAQ #6281:

• You must choose your targets (up to 4 cards in trashes) when you activate the ability and place it on the chain.
• Because the card is still on the board at the moment you choose targets, it cannot be one of the targets in the trash.
• Once you pay the cost by killing the gear (moving it to the trash), the ability is already on the chain with its targets locked in.

Additionally, as established in the provided FAQs, "Kill this:" is an activated ability where killing the card is the activation cost. You cannot target the card itself to be recycled because it must be a card already present in a trash zone to be a valid target for the recycle effect.