Things to do alone in London?

I legit have so much time on my hands and I have a job so I’m not short on cash and literally could go out any time of the day but I just don’t know where to go.

I’m going to Portugal next year on a solo trip and I lack common social skills so I guess I have to build up my confidence this year at all costs or I will struggle and won’t have a good time in Portugal.

I know museums are good, maybe bike riding, cinema, park in Greenwich or main London.
I don’t know where else to go, I really want to meet new people too and make new friends and hopefully meet someone nice if possible (not at all my main concern).

Any ideas?