What is the ruling on interrupting prayer due to obsessive whispers (waswas), while giving the impression to the congregants that one is continuing, and then repeating it secretly? And is giving the impression to the congregants that one has not interrupted the prayer or is not afflicted with waswas considered hypocrisy (riya') that necessitates making up missed prayers? And is raising one's voice during the tashahhud and then lowering it when someone looks at you considered hypocrisy?

The prayer of the questioner is invalid because he severed his intention, but the prayer of the congregants is valid because the reason for the invalidation of the Imam's prayer was hidden from them. Anything that invalidates the Imam's prayer and is hidden from the congregants does not invalidate their prayer. Your single takbir and raising of hands does not invalidate your prayer if you made the takbirat al-ihram (definition) while standing. There is no showing off in not raising the hands for bowing or in lowering the voice during the tashahhud (definition). You are not required to repeat the prayers.