Follow this steps to update JoomMedia from J3 to J4 correctly.
- Make sure to update your joomla website to latest version 3.10.x
- Makue sure your JoomMedia version is the last one (v1.3.8) in joomla 3 series
- Disable all JoomMedia plugins from Plugins Manager
- Update Joomla 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 JoomMedia v4+ then install on your updated website or use Joomla updates manager.