Since its linux you can sync whatever you want with no restrictions. There is an infinite number of manual options that you can setup for yourself. For an automatic sync of calendars/contacts/files/etc setting up a personal nextcloud server is a good option. You don’t need to use KDE connect with the KDE desktop, there is a gnome extension called gsconnect that will connect with your kde-connect enabled devices, but this doesn’t provide calendar and other syncing stuff that you are looking for and also doesn’t have a client app for linux mobile devices yet