You can't withdraw Bitcoin on the lightning network to on-chain wallets.
You'll have to do an atomic swap to move your Bitcoin from lightning to on-chain. You can do atomic swaps from Alby and any other lightning wallet. I use Boltz.
When nostr:npub1getal6ykt05fsz5nqu4uld09nfj3y3qxmv8crys4aeut53unfvlqr80nfm will have. an option to withdraw sats to on-chain wallets? #asknostr
Discussion
However, Alby Hub has onchain wallet built in (naturally) and sats can always be withdrawn!
you can open channels with these funds , and sats from channels closures fall back to that onchain wallet