I was thinking about a theoretical attack vulnerability. Suppose that if the daemon that mines the block is able to see transactions in clear text, then it would be able to log this information in a side-database? Is this possible?
Pending transactions are in a transaction pool, which is publicly available. See for example this page.
Each daemon has a copy of that transaction pool and, when finding a block, will include some of the transactions in the block before pushing it to the network. The details of the transaction, (a) as created by a wallet client, (b) in the transaction pool and (c) in the blockchain once it's included in a block are the same.
So your question essentially asks if Monero transactions can be decrypted, which has been answered in other places, such as: What privacy issues did Monero have and still has?
I went to #monero Slack channel, and received these answers:
… the destinations that the client sees are "encrypted" and not linkable to the monero receiving address you use
… the daemon would only see signed transactions, not the info and only someone with the view key could see what's in there
correct, the daemon only receives already-complete transactions
So, the theoreticized attack is impossible, because the Monero daemon (not even the one transmitting the transaction to the network's mempool) never gets to see that type of clear text info.