Have deeds been nullified after disbelief, and does asking about that constitute disbelief due to a lack of trust in Allah's forgiveness for all sins, and what is the solution?

Apostasy-inducing whispers do not harm whoever detests them and recoils from them. The cure for them is to ignore and disregard them, and to seek refuge in Allah from Satan. One must adhere to Allah's law, maintain acts of obedience, and avoid sins, for abandoning prayer and intentionally breaking the fast in Ramadan are grave sins. One must make up for missed prayers and fasts. If apostasy occurs – Allah forbid – sincere repentance is obligatory, for Allah forgives all sins for whoever sincerely repents to Him.