Follow this steps to update JoomGrabber from J3 to J4 correctly.
- Take full backup of your website using Akeeba backup or using cPanel/Plesk backuping system
- Make sure to update your joomla website to latest version 3.10.x
- Makue sure your JoomGrabber version is the last one (v1.6.x) in joomla 3 series
- Make sure to disable all JoomGrabber plugins
- Update your Joomla website from 3 to Joomla 4 , read this article: https://docs.joomla.org/Joomla_3.x_to_4.x_Step_by_Step_Migration
- Once website updated to Joomla 4 , go to joomboost downloads and download JoomGrabber v4.x then install on your updated website or use Joomla updates manager.
- Enable again JoomGrabber plugins.