I lost all of my social network during 2020. Being almost 40 and with the current situation still in progress, I don't even know where to start. I have no social contact outside of remote work and some sport activities.
It's one of the more challenging parts of life anyways as YMMV. Some people have loads of contacts and friends, others have enough with only a handful of close ties. There's no catch-all that works for everyone. And I think it's important to acknowledge that everyone has different individual needs.
Building a sturdy social network with a variety of contacts isn't something you do overnight. Rome wasn't build in a single day either. This takes time. And yet, you might surprise yourself one year from now. A lot can happen in 365 days if you decide to put your shoulders under this.
> I don't even know where to start
Group activities are a great way to meet people.
Group travel, classes / workshops, local social / cultural communities, outreach activities,... For instance, I enrolled into cooking classes for a few years, which was a great way to meet people and have great food. Many non-profit organizations do stuff like guided walks and tours, visits to venues, organise workshops and so on.
Volunteering works too. Doesn't have to be charity. Working with youths is a pretty great way to get involved in a local community. Even in your late 30s.
What worked for me in the past was just walking into a community center and striking up a conversation with people who are working there: What are they about? What do they offer? Are they doing cool stuff? If you show interest, they will pick up on that.
One challenge is to get out of your comfort zone. Try out things you haven't tried before. Like, try following a first aid, dance or yoga class if you haven't. Don't get stuck in an area related to work or older hobbies you have.
Be mindful that not all things you explore will work out for you. You might feel that some stuff just isn't for you, or that the group dynamics aren't a match. That's totally valid. It's fine to drop an activity for something else if you feel disengaged.
As for making friends: those are actually a side effect of the above.
One doesn't make friends out of the blue. You put yourself out there first, trying and exploring the world, following your own interests. And as you do so, you will hit upon people who might become friends. And in due time, some of them might even become close friends.
Personally, I'm in a similar boat as you. Intend to put myself out there over the next few months, try some new things I have on my mind, and spend less time in front of digital devices as I did in 2020.