Hi Bro, understand how you feel

Making new friends at adult stage is not easy and if i may say so, you're probably more introvert and take longer to warm up to people. Else you won't be asking this questions here.

Like people say, try to join clubs or activities that you like.

At least there you can meet people with common interest and start building new connections.

I end my post here with this statement that I hope you won't feel offensive

You will need to invest time to build new connections but don't invest too much emotions

Just because people are friendly to you, it doesn't mean that they are your friends... and vice versa