Why do you specify "out of grade school"? Isn't the fact that the mall is the go-to for grade schoolers just as big a problem? Where are kids and adults supposed to hang out in a group without having to host in their small home?
On the flip side, the indoor malls used to provide a public air conditioned space people could flock to, at least on the weekends. Much like movie theaters used to be by themselves. Now they're being torn down, and sprawling outdoor malls with mister systems are constructed. In some ways better, in others not so much.
In the end, will it really matter? The older I get the more I want to move to a smaller town and work remotely. I miss people being friendly and in less of a miserable rush overall.
Kayaking (not whitewater) and fishing are my two favorites especially if you combine the two. I usually talk to any fisherman I see and people come up to me at the ramp to chat.
A closer use case would be neighborhood centers, but in my area, those are mostly closed in the evenings or at least reserved for private use.
The local mall used to open early for older people to meet and do their daily exercise walks. Depending on the climate and time of year, parks are not always usable.
People grilling, kids playing, walking/running/biking/kayaking/paddle boarding and people just sitting and relaxing. Lots of social interaction.
If you’re out of grade school a mall is not an appropriate place for social interaction.