Is the data stored on the blockchain immutable?

Yes, the data recorded in the blockchain is almost immutable. As you know, the data stored in a blockchain is called a block. Each block is associated with a hash value. Now each block contains not only its own hash value, but also the hash value of the previous block. If any changes are made to the block, this will change the value of the hash function. Consequently, if you want to tamper with the data in one block, you have to change the entire block chain, which is almost impossible.

But in case of Filecoin we have PiBs of data stored that can be changed (as Filecoin is PoR blockchain). But it can be changed only by the person who've uploaded.

What is the best way to store your data on blockchain?