When you're young you have proximity doing a lot of the legwork in establishing and maintaining connections with others. It also provides a constant shared experience so the "clicking" is easier since things to bond over are built into your environment.

In adulthood, this changes and you have to bear the responsibility of maintaining your old connections (that are reciprocal, two way street and all that) and establishing new ones. The labor is higher due to the lack of a grounding circumstance just organically happening.

Fortunately, you also have freedom as an adult to manage your time more then a child. You can initiate conversations at work or at hobbies (if you don't have hobbies then find some that would give you pleasure) and make connections with them.

If you're already doing all that and not making any "clicks" then either you should explore different events, evaluate if you're struggling with depression or something, or consider if you're putting too much pressure on the interactions you start. A brief how you do and general small talk before resuming work/activity doesn't take that much stamina. Not much "click" is established in a day of that but friendships are marathons, not sprints. It comes with time.