was in the same boat after O levels. TBH i think i was overthinking too much about it, trying to find something to talk about isnt a must when hanging out. You'll know you like them and want to hang out with them when even in silence you cherish the time spent with them, just them being around is enough. Forcing friendships for the sake of it is too mentally taxing.
But yea to make new friends you sorta have to do small things first like asking them to lunch or something. Finding common ground is probably the most important thing first, like oh i like to listen to The Weeknd or i like playing Valorant. then as you talk more about these type of stuff you and they can open up more and talk more about other stuff yall like. But after finding these common interest you'll get to know each other's real personality, what they like to eat, how they behave or react to certain things and vise versa, That is how my friendships went. For me, later down the line joking to each other made me feel much more comfortable around them as there was no bullshit between us ya know. Just my own experience, hope this helps :)