Oh, I feel some scope creep starting... What fun!

First, if it is a stand-alone book, you need to resolve the big conflict you started. The climax is the beginning of the end - that moment where everything comes together (often in a fantasy book it's that final battle, or in a romance it is where the two finally can be together). The end after that is finding the resulting changes.

If your tension is still going up - what are you feeding into, and does it need to be resolved in this book, or is it going to be a multi-book thing? Because even a first book in a series will often have some sort of 'happy for now' though you know the villain/situation is still out there. I would think the climax is when the tension becomes so high that you need to let the characters find a resolution, even if it isn't going to stick.

https://thewritepractice.com/climax-of-a-story/