Also, in places with significant winters (including Northern Europe) parks aren't an option in winter.

Northern Europe seems like the kind of place that would realize this is a problem and invent some kind of community building which was open in the winter and had a shared kitchen, a stock of board games, a court for indoor sports, etc. That's certainly not going to happen in the US.

I'd say the qualities of the average American park leaves much to be desired, when compared to NYC Central Park, San Diego's Balboa Park, or SF's Presidio.

In suburban areas, the municipal park tends to be a monoculture of grass plus maybe a playground, a parking lot, and if lucky, a usable bathroom. Regional parks are often nicer, with amenities like pickleball courts or a BMX park, though asking for benches (not rocks or concrete verges, but actually bench seats) and shade might be a stretch.

My point is that the USA has fewer parks and public squares than it ought to. I don't mean just a place to go jogging or to push a stroller along, but a proper third space where people actively spend time and create value at. Where street vendors congregate because that's also where people congregate. A place that people -- voluntarily, not by necessity, eg a train station but not to catch a train -- would like to be. A destination in its own right, where even tourists will drop by and take in the air, the sights, and the social interactions.

Meanwhile, some parts of the USA actively sabotage their parks, replacing normal park furniture with versions that are actively hostile to homeless people, while alienating anyone that just wants an armrest as they sit down. Other municipalities spend their Parks & Rec funds on the bare minimum of parks, lots that are impractically tiny. Why? Because a public park can be used to exclude registered sex offenders from a neighborhood, leading to the ludicrous situation where whole cities are an exclusion zone. Regardless of one's position on how to punish sex offenses, the denial of housing and basic existence is, at best, counterproductive.

So I reiterate: the USA might have a good quantity of parks, but not exactly good quality of parks. People will socialize online unless they are given actual options to socialize elsewhere. And IRL options would build value locally, whereas online communities only accrue to the benefit of the platforms (eg Facebook, WhatsApp) they run on.

The problem is in parks everyone is too spread out to talk to strangers. There needs to be a park with a bar to bring everyone together.

Depending on the gym, some are a lot more third-spacey than others. I've been to a smaller gym where people just hang around after their workouts to socialize, with occasional impromptu dinner outings when the gym closed for the night. I miss that place. You still meet people at bigger commercial gyms, but it's not the same.