This is actually a loaded question. The short answer to your question is of course: Yes, they are quite similar, in the way portuguese is similar to spanish. But, also, yes, if you want to talk to a Dutsh person (in Dutch rather than English) you need to learn the language, because the similarities will only get you so far.
A more hidden aspect of your question is really an intercutural one. I say this as a German person, who grew up in the Netherlands and speaks Dutch fluently. The Netherlands (pre-Covid of course) has a lot of tourism from Germany. I used to live in a very touristy area, and I can tell you that many of the natives will have learnt German, because that is just what you do, when you live of off tourism. But then again German tourists can fell very entitled and then they will assume everyone speaks and understands German. And that creates some tension obviously.
This depends on the situation of course. If there is a problem and you just have to communicate somehow and one person speaks only German and the other only Dutch, it might work and that's ok. But if someone just goes to the Netherlands and speaks in German because they just expect to be understood, that is much less ok.
And then there is the question of where in the Netherlands you are. The farther away you are from the German--Dutch border the less likely it is to find a German-speaking Dutch person (unless you are in a touristy area). Keep in mind there are also still those who have anti-German resentments, not because of entitled tourists, but the war! On the other hand, and this to me is surprising, many older Dutch people will have had German lessons in school and this has shifted towards English in recent decades. So, you never really know.
If you are in a region very close the border, there are many people, who will commute to the other country regularly and here you will find many speakers of both languages. And then there are regional differences in the way Dutch is spoken. The more to the south-east you go, the stronger the influence of German will become (if you want to see it that way).
There is also a regional dialect, which is a quite confusing mix (to me anyways) of German and Dutch and this is spoken in the most south-eastern part of the Netherlands (Southern Limburg) and the area of Germany close to it. Anecdotaly, the people in this region will understand each other better that they will understand someone from their respective country. And while it sounds very German-esque to me, it is not.
Long story short: If in doubt, speak English, just to be on the safe side.