I have few transactions and I'd like to get the from addresses of these transactions. I couldn't found anything like an API or RPC endpoint which returns from addresses. Any advice or help appreciated, thanks in advance!
If you are referring to transactions that were included already in the blockchain, please note that the transaction hash is not a unique identifier for a transaction in Polkadot. Hence you can't expect to simply query them by their hash.
However, if, apart from the transaction hash, you have the block number in which it was included, you can do something similar to what was proposed in this answer. In this case, the sender address is showed as in the signer field as as a SS58 formatted address.