Is it obligatory for someone who has embraced Islam to declare the Two Testimonies aloud after having been Muslim for some time, praying, fasting, and striving in the religion?

Doubt about uttering the two declarations of faith (Shahadatayn) after two years of worship and diligence is a whisper from Satan. The brother has repeated the Shahadatayn many times during this period, whether through the Adhan (call to prayer), saying "La ilaha illa Allah, Muhammad Rasul Allah" (There is no god but Allah, Muhammad is the Messenger of Allah), or uttering them in the Tashahhud during prayer. Prayer itself is considered an entry into Islam, as scholars have said concerning the disbeliever: "If he prays, he is legally considered a Muslim." This is supported by the Hadith: "Whoever prays our prayer, faces our Qibla, and eats our slaughtered animals, that is a Muslim." One must beware of whispered doubts (waswasa) and treat them with remembrance of Allah (dhikr) and by not paying attention to them.