You need to find a thing that is bigger than yourself to be a part of. And then show up and be willing to pitch in.
Other adults who know that adult friendship is important will be there.
The rest sorts itself out pretty fast, because almost everyone enjoys the company of someone who is willing to put themselves out there, even a shy, awkward person.
There are of course people who can't "show up" so easily -- people with limited mobility, people who are physically severely isolated. But the internet does offer some spaces where those people can have a lot of what face-to-face friendship offers. Again you just have to find a shared activity and show up.
“I have a hard time making friends” may be eventually interpreted as “I have a hard time putting me in situations to be able to make friends” just 2 sides of the same coin, isn’t it?