Questions & Answers about أنا لا أستطيع أن أمشي اليوم، لكن صديقتي تمشي إلى الحديقة في المساء.
Yes. أستطيع already tells you the subject is I because of the prefix أ-.
So أنا is not strictly necessary here. You could say:
لا أستطيع أن أمشي اليوم
and it would still mean I can’t walk today.
Including أنا can add:
- clarity
- emphasis
- a more explicit contrast with صديقتي later in the sentence
So أنا لا أستطيع... لكن صديقتي... feels a bit like As for me, I can’t..., but my friend...
In Modern Standard Arabic, لا is the normal way to negate an imperfect/present verb.
So:
- أستطيع = I can / I am able
- لا أستطيع = I cannot / I am not able
A native English speaker may wonder whether Arabic uses something like not after the verb, but in Arabic the negative usually comes before the verb.
After verbs like أستطيع (I can / I am able), Arabic usually uses:
أن + imperfect verb