No open source, then I'm not playing.

I use Zim wiki for everything just now and I don't like it. I'm in the market for a replacement, and would even pay like with how Immich does it.

Unless the source code is available or you put it into legal escrow for when you go bust/abandon the software†, I will not invest my time and data into a system where I am entirely dependent on another organisation or service.

† And you will go bust or abandon the software before I die!