Can I rely on my full node to always have the most recent blocks? I have a full node running and I am using ZMQ to let me know when new blocks arrive. How can I make sure that this block that my node received is a valid block written in the blockchain ledger and it is not an orphan block?
Can I rely on my full node to have the most recent blocks?
how can I make sure that this block that my node received is a valid block


Bitcoin Core will only announce (through ZMQ) blocks that change the tip of the best-known valid chain. This implies they together with all their ancestors are fully valid.


  and it is not an orphan block


At the time it is announced, you know that it is part of the best-known valid chain. Of course, it's always possible that a better alternative branch is received later, which reorganizes the old one you heard about. In that case, you'll receive a new ZMQ notification for the new best tip.


  Can I rely on my full node to have the most recent blocks?


No, of course not. The speed of communication around the earth is finite; if a new block has been found somewhere on earth, there is no way you can know about it before it's had time to propagate to you.

Even ignoring that, it's always possible for the nodes you are connected to to be slow, broken, or malicious, in a way that prevents them from propagating blocks to you.

The only correct way to think about this is that there simply is no such thing as "the best/most recent block", and every node is continuously trying to catch up with new information. In theory, you never have any guarantees. In practice, usually nodes learn about blocks within seconds, and if it takes way too long (say, hours), you'll know something is wrong.