That doesn't solve parent's (and my) problem.

I have collections of tabs in different windows and I assign those windows to different spaces. Every time I reboot Chrome all windows are assigned to whichever space is active when I launch Chrome.

I seem to recall that Chrome used to remember these assignments, so maybe it's not a macOS problem, but rather a Chrome problem...?

This is also how I use Chrome with spaces. I’d love someone to solve this problem.

Btw. Zen Browser or Arc have great management of spaces in the browser. You can quickly switch between profiles without unloading them. So you can be even on a call using work space and switch to personal space. This way you don’t need to have separate windows per profile unless you need to see the content of both at the same time.

Yes! Would love a solution to this.

I'm of course assigning apps to specific spaces. But my browser has to be in all spaces. MacOS still doesn't remember which window is where when the app restarts or the OS reboots.

I’ve been using the Orion Browser a lot recently. Each profile pretends to be its own app as far as I can tell. You get separated spaces for work and private and links open in the last used window. This might solve your issue of assigning multiple windows to different spaces.