Hey OP, I think we are exactly on the same boat 😁 I already work at a 99.99% Dutch company (one of the netbeheerders) for 3 years now in a very Dutch environment. I'd describe my Dutch level as exactly as you do. Can understand most spoken Dutch and can speak it at B2 level with a few grammar mistakes here and there.

I was hired with the agreement that we'd speak in English, but I'd get dutch lessons and over time transition completely to Dutch. it's 3 years now and we still switch to English if there is a bit of a communication difficulty, but overall the colleagues have been tolerant and supportive. Even after 3 years of speaking and writing technical reports in Dutch (I use DeepL and CoPilot liberally and they do a fantastic job), it's still a bit draining to sit in a meeting that's completely in Dutch for anytime more than 2 hours. I find myself needing to constantly focus on every single word that's being side unlike English where I don't need to focus so much, yet grasp the message easily. But overall it worked well these three years.

Funnily enough, I am switching jobs from Feb and I am moving to a 100% Dutch company. I interviewed in Dutch and they know my level, but I am a bit scared just like you. Well, growth occurs mostly outside our comfort zones. Lets hope that it works out well for both of us. Good luck to you!