The actress was out and about in NYC Thursday, walking hand-in-hand with Jonathan Davino -- to whom she's been engaged for about 2 years now, and dated even longer going all the way back to 2018.

As you can see, they're 2 peas in a pod ... and SS flashed a big smile with her man. He was looking pretty happy too -- and who wouldn't be with someone like Sydney at your side?

Sydney's blown up over the past year as an A-list star, and she continues to turn heads at just about every event she shows up to -- for good reason, too, as she's absolutely gorgeous and is probably one of the biggest blonde bombshell actresses we've seen in a long time.

While everyone seems to be thirsting over her lately, Davino is often tucked away in the background -- and yet, he's clearly confident in the relationship ... as is Sydney, it seems.

Remember, there was a lot of speculation last year that something might've been going on between her and her costar Glen Powell ... but she and Jon weathered the storm, and they're going strong. He even accompanied her to the Oscars a couple weeks ago.

Another fun fact ... they're in business together -- she and Jon co-produce projects under her production company, Fifty-Fifty Films ... so, they're obviously very tight and in lockstep.

Unclear how exactly they first hooked up ... but Jon's been in the picture pretty much all throughout Sydney's meteoric rise in Hollywood. Despite her growing fame, the dude doesn't appear to be bothered one bit ... and ditto for Sydney.

What's also interesting is that she and Jon are incredibly private ... not much is really known about him or their dynamic. In any case, she's smitten with the guy.

Lots of dudes out there may or may not be aware of the fact she's off the market -- but if you didn't know ... here's a reminder -- there's no chance of shooting your shot with her, 'cause she's happily taken!