Padma Purana :
"The legend of Shri Ram has been described in Shat-Koti Ramayanas, if
any differences are seen anywhere in those ancient stories, then wise
ones have suggested that it was because Shri Ram had performed his
pastimes diversely in different kalpas."
Ananda Ramayana :
"Due to descent of Bhagvan Shri Ram again and again in different kalpas, infinite incarnations of Him have taken place. Among those infinite incarnations, there had also been differences at some place in His pastimes.
The extremely amazing pastimes and valorous exploits of Bhagvan Shri Ram are spread across millions of Shastras. Sage Sukadeva is going to describe that infinite glory of Shri Ram in just two chapters and He summarizes the same in His single shloka.
So as you can see clearly the reason for so many Ramayanas, there evidently is no need to doubt which one is true, because the universe is not 100% predetermined. Things are randomized, but in a trajectory. A few distortions, alterations and dynamicity are ever-present in the hurricane, which is ultimately aimed at a single destination. Therefore all the Ramayanas are true, because they took place in different epochs.