Yes, as much travel as you like within the validity of the pass, as long as you’re not resident in Belgium or NL.

Bear in mind you’ll have to pay €20 reservation fee each journey on the Thalys, or a small supplement if you travel on the Intercity Direct.

I have to correct a few small points :

Thalys has a 27€ mandatory reservation (+2€ fee per person per train). There is a very limited passholder quota so trains sell out days or weeks in advance.

The IC Direct does not require a supplement. Seat reservations are not possible either : sit wherever you want.

-> the IC is the way to go :)

The B-Europe and Eurail Reservations service is showing €22 + booking fee for the Thalys Amsterdam - Brussels in second class (€27 in first).

Railplanner also shows a supplement required for the ICD. If that’s wrong, then perhaps one of the Eurail staff can change this.

Ah yes it's 22€ between Belgium and the Netherlands, 27€ Belgium - France and 32€ for 3 countries.

The info about the supplement should've been removed in a recent update. The subject has been discussed multiple times especially by @rvdborgt who contacted NS. Here is a link :