Anki crashed and giving Fatal Error, unable to open

Notice how it mentions a PoisonError at the bottom? That indicates it’s not the first error that has occurred. If others pop up, please check them, and paste the one that doesn’t mention PoisonError.

If no others pop up, you should be able to locate the original error via the console:

https://addon-docs.ankiweb.net/console-output.html#showing-the-console