I have not as yet tried to do the upgrade what happens to the old OC applications that were not “core”. For example, Bookmarks and ownotes?
Thank you for your interest into Nextcloud. Apps, which are compatible with ownCloud 9.0 are also compatible with Nextcloud 9 You just need to upgrade and reenable or reinstall the apps from the apps menu. Currently, Nextcloud also uses the same app store as ownCloud, so the apps are the same.
Everything works fine…even the experimental apps are available in nextcloud 9.0…