For the love of god, read the manual.
Don’t expose your entire system with SMB..
Plex has migrations instructions on their support site..
The snapshots you have are valid, they aren’t dependent on the FreeNAS install, they are pool based.. roll back to a date before the move. Install a fresh FreeNAS 11.2U1 and load the configuration from your earlier installation.
Then set up a new jail for plex, make a snapshot just after installation. Dump the database or what ever plex tells you to do and migrate your old instance to your new jail. Take another snapshot when you are done with that. Now you set up media folders and permissions per the guides here on the forum. Do not set 777 system wide!!
Do all this from an SSH consol, you can ssh from Windows CMD or cmder by installing WSL on Windows 10. Earlier versions should really be updated, but if you right out refuse you can use PuTTY or an equivalent.