So much has changed that I wouldn’t try copying project templates directly.
Instead, I’d suggest using your current version of Scrivener to create a new project from the template you want to transfer. Open that project in Scrivener 3, edit as necessary, then use Scrivener 3’s Save as Template command to create a new template.
I’d recommend taking a look at our upgrade guide for Scrivener 2 users, as Scrivener 3 has some very significant changes. You can find it here:
literatureandlatte.com/scri … date-guide
Katherine