It is possible to self study A levels but, as a strategy, it generally results in a better outcome if you’re already experienced in studying and know what is expected of you and what your limitations and strengths are as a student.
I would strongly advise looking into study options that provide you with some structured feedback. Humanities subjects are not advisable as these are not subjects you can learn in the sense of just processing information. Languages, however, would potentially be accessible if you joined a language group in your area and Maths has plenty of options for self study, some free, some not. I would stay away from sciences too as it’s almost impossible to get the lab experience.