Can someone see I am using the Nym network?

Yes — but only in a limited sense.

The NymVPN API and the list of Nym gateways are public. This means that someone monitoring your connection could observe that you are connecting to a known NymVPN gateway or accessing the API — just as with traditional VPNs, whose server addresses are also publicly available.

However, what you are actually doing remains fully private:

In both dVPN and mixnet modes, your traffic is protected by onion encryption, meaning that no attacker can see the content of your communications.

In mixnet mode, your traffic is mixed with cover traffic, making it impossible to distinguish real activity from background noise.

In short: while observers might know you are using the Nym network, they cannot tell what you are doing, where you are going, or even whether a given packet contains real data.