Are monero transactions still anonymous when using a payment ID? For example, I send to coins to a address with a payment ID. Is this transaction still 100% anonymous impossible to track?
Yes. Using a payment Id still maintains Monero’s privacy features
A payment Id allows the receiver to keep track of incoming payments from specific sources.
The best way to use a payment is to integrate it directly into a wallet address by creating an integrated address. This will generate a unique address with an integrated payment Id that the receiver can give to a specific source so the receiver can keep track of a payment from that source.
Note: when transferring monero to your wallet from some exchanges, they will ask you for a payment id in a separate field to the address, in this case you should use your original address (not the integrated address) and the payment id separately