Is repentance from polytheism and disbelief valid and obligatory, especially with recurring whispers (waswas), and does this include apologizing to those who were wronged or who witnessed the sin?

"Insulting the Lord is among the gravest calamities. Whoever insults Him, whether in jest, seriously, or mockingly, commits an act of disbelief. Since you are unsure of your intention, this is a whisper (waswasa), and there is nothing against you as long as the possibility exists. Turn away from these whispers. Whoever utters words that might indicate apostasy or something else does not become a disbeliever thereby, for the Sharia principle is to avert a legal punishment from a Muslim whenever possible. The cure for whispers is to completely disregard them, for surrendering to them only increases them until they drive a person beyond the realm of the rational. They originate from Satan."