In case of a grouped transaction, how to determine who sent what to whom? Trying to understand how grouped transactions work, I came accross the following transaction on blockchain.com :


There are many senders, and even more receivers. For instance, the first sender on the picture could have sent 1 BTC to the first receiver, 10 to the fifth, and so on...
How can I determine (if it is possible) what amount sender A sent to receiver B , instead having the balance for each participant ?
How can I determine (if it is possible) what amount sender A sent to receiver B , instead having the balance for each participant ?


You pretty much can't. Often times, transactions like these are created for the purpose of making it difficult to determine which inputs are sending money to which outputs. Such transactions are called CoinJoins, so named because multiple people are joining their coins together in one transaction.

There are some techniques for determining which outputs are created by which inputs, but these techniques are not foolproof and often make assumptions that are not guaranteed. In fact, many software that make Coinjoin transactions are designed to make those assumptions non-viable and thus break such analysis so that the participants in the CoinJoin have more financial privacy.