Joomla 4 is now supported - How to Upgrade
Version 4.7 of Ignite Gallery was released on Monday the 30th of August 2021. This version works in both Joomla 3 and Joomla 4.
You can install version 4.7 of the component/module/plugin on top of any older 4.x or 3.x component/module/plugin. All php/css files will be overwritten, but no content will be lost.
If you are upgrading you site from Joomla 3 to Joomla 4, please upgrade Ignite Gallery to version 4.7. No extra steps are required, version 4.7 of the gallery works in Joomla 3 and Joomla 4.