if yes, how do i create a back up?
Usually website host offer this service, you can contact them for details.
If they don’t, you can use a backup plugin:
https://www.wpbeginner.com/plugins/7-best-wordpress-backup-plugins-compared-pros-and-cons/
what about generateblock, classic editor and All in one SEO? do i deactivate these as well
They belong to the “all plugins except GP Premium” group, so yes, deactivate them all.