No ferries in Amsterdam are included in the pass.

Are there any other benefit like discount in Museum etc?

Passholder discounts, etc can be found here https://www.interrail.eu/en/plan-your-trip/pass-benefits also in railplanner app under More>Benefits.

The very short (2 mins or even less) foot/bike ferries just behind CS (there are 3, 1 is a bit longer and only mo-fr to an industrial area) are FREE-for anyone.

FREE is also the open-air ´Zaanse Schans´ (those cutesy green wooden small houses, made to look similar to medieval housing) close to a suburban stop along the Zaanlijn. But perhaps the similar looking and high-rise HTL beside Zaandam station is already enough.

If you can manage to have yourself enscribed in the pubic register of people who live there and age >65 you can get a free card with monthly coupons for various free entries or ultra-cheap. If you can also prove your income is ´below poverty line´ you also get free trambus season.

IN spring=not now, the tulip fields that are so magnetic to foreigners can be viewed out of the trains Haarlem-Leiden.

In summer various smaller and partly also cutesy looking smaller towns with ancient centres also hold weekly ´traditional´ markets, places like Hoorn or Schagen or Alkmaar (cheese market on FRI-perhaps even all yr) have excellent (in normal conditions, not really now) train links to that magic city that is since this yr actively trying to ban tourists amap. It also charges about the highest tourist-tax on top of HTL-prices in the whole of EUR.

There is a ferry at Amsterdam Central station to get on the oposite side and is for free, but is only 1-2 minutes ride.

You do get a nice discount on the Stena Lines ferry from Hoek van Holland (NL) to Harwich (UK) with Interrail/Eurail, but that’s not Amsterdam...