There is not really a migration from J3 to J4. You just have to make sure all your components & templates are J4 ready or compatible. There is a checker when you try to update that will tell you about any issues before you update from J3 to J4.
That type of migration works fine only on sites that uses only articles and categories for data. If you use 3rd parties components you will also have to follow their guides for migration J3 to J4. Virtuemart is particularly complex, as also Widgetkit which looses large part of settings when going from W2.9 to W3.
Virtuemart can be updated easy, plugins for VM must work on Joomla 4 so check it.
I have updated many sites and complex. You need to update all joomla 3rd party plugins with version working on Joomla 4. Uninstall any plugin module or component not working with Joomla 4 first
If you are unsure about compatibility I always make full site Backup Using AKEBA and then simply try upgrade locally with XAMPP to test upgrades. Usually takes 10 Min to setup test case and liek @forty said do uninstalls and upgrade of all components and plugins.
There is not really a migration from J3 to J4. You just have to make sure all your components & templates are J4 ready or compatible. There is a checker when you try to update that will tell you about any issues before you update from J3 to J4.
There is not really a migration from J3 to J4. You just have to make sure all your components & templates are J4 ready or compatible. There is a checker when you try to update that will tell you about any issues before you update from J3 to J4.