Yeah... good luck with that.
Not to say that people don't make friends outside work, but there are many variables involved with that.
But just use Meetup.com, right? Sure, if you want to spend a few hours with people of retirement age, not if there's anything wrong with that.
Not having friends is just the surface level of the issue. If all you want is friends and friends alone, then that really isn't that hard to arrange.
If the use of "friends", however, is those who are in your age cohort as well as romantic possibilities, that's an entirely different beast that can be ironically difficult to conquer once college life has been long since left in the dust.
For many, if not most, the office was the deciding factor as to whom you would associate with in adulthood. Plenty of people have met long time friends as well as their husbands and wives at the office. With remote work, this is extremely difficult to pull off. I've been fortunate to have made one or two good friends through my years of remote work, but I had 100x more social opportunities back when I worked in a physical office. I miss the fact that I could have a best work friend kind of like how I usually had a best school friend as a child. But it's usually impractical to make such connections when all you have is Slack and Zoom, neither of which are good for shared 1-on-1 experiences. There's no chance to say "Hey, wanna run to Starbucks with me?"
I wouldn't give up remote work entirely, but I'm finding there's a lot left to be desired that would be met in an office. The office is the missing variable that gets people to spend sufficient amount of time together on shared goals. That's not easily going to be replicated by introducing yourself to random people in town.