With YourSites 1.9 you can run a pre-upgrade checker against each of your client sites.
After selecting sites to check select the menu item from the 'Core Software' or 'Joomla' menu item
Client sites check their compatibility status
Preview the basic extension compatibility in the status popup
Full information can be seen by clicking the Joomla icon in the site status icon block
Here you can see the Required PHP and DB Settings
and the recommended settings
and extension compatibility
We use the information provided by the extension publisher about compatibity of extension versions with Joomla 3.10 or 4.0. You should use this as a guide to likely compatibility since we cannot guarantee that this information is correct or that the extension is actually compatible. You will need to confirm with the extension publisher that the extension version is compatible and ideally test the upgrade on a backup/clone website to make sure there are no unforseen problems and at the very least make sure you have quitable backups.
We love every single one of our users, without you YourSites simply couldn't happen! So we would love a review at the Joomla! JED so we can let others know about us too, please take a minute to write a review:
https://extensions.joomla.org/extension/yoursites-manager/
If you feel you have something negative to say, we would implore you to speak to us first, as we really really don't want anyone to be unhappy!