I'm looking for a venue idea that is unique and special for 60-80 people in New York city preferably Brooklyn with an outside garden section for this fall.
My daughter found an Italian restrurant called Frankies 475 Spuntino but they don't allow amplified music. It could be lovely as there is a prior blacksmith store with brick walls. You get the idea. Any suggestions would be appreciated.

How about the Brookly6n Botanical Gardens?

https://www.bbg.org/visit/weddings-events

If you're not completely opposed to going just a little bit outside of Brooklyn, I HIGHLY suggest you check out The Foundry in Long Island City. I came across it in wedding venue search and was heartbroken to learn I'd have too many people to fit there. Given that you mention "outside garden section" and "brick walls", I really think you/your daughter will love the Courtyard and Greenhouse spaces.

The Foundry

Our son and dil were married a couple of years apo in the Brooklyn Winery. Great setting with very good wines.

I guess the OP eloped.

Thank you for your reply

Thanks We've looked at the foundry and it being a raw space and not having a lot of time we did decide to go with Frankies 475 after all. We hoping to plan dancing somewhere else.
The bonus is they make their meatballs with nuts and raisins just like mom used and the date we picked is her bday. Mom passed several years ago at age 100.

Try to check out The Palm House. Been there last year. Their reception and garden area are incredibly beautiful.

My daughter changed the venue to old field club on Long Island. Barn like on a channel with a dance floor which Frankie’s didn’t have.

The Coney Island Pier is a good place to get hitched. Heck, you could even jump into the water for good luck!
Then walk over to Nathan's for hot dogs, then consumate the marriage on the beach... but after 9pm that is.