ESP header and trailer I investigated the IPsec Protocol.
I am wondering if I can remove/reduce any field to save space,
is there a way to save overhead in ESP packages?
I am wondering if I can remove/reduce any field to save space, is there a way to save overhead in ESP packages?

Well, there was an old IETF draft here to address this very problem; however it didn't get enough traction in the IPsecME working group (for the complexity it has, it doesn't save that much space) and thus was abandoned.
Sticking to standard IPsec, well, you could remove the space used by the nonce by using RFC8750; that saves 8-16 bytes (depending on what transform you were previously considering)
And, you could decide not to use an authentication transform (thus eliminating that overhead).  On the other hand, that could bring up the possibility of active attacks; I can't recommend it.
And, as you are probably aware (but I'll mention it anyways) if you're protecting traffic between two endpoint devices, transport mode will allow you to not include an IP header in the payload data (thus saving you another 20-40 bytes).