Thank you for drawing my attention to the answer re Sydney Pro and that the page builder pages will be ok on migration. However that does not anwer my question directly so:
i) Regarding the FREE Sydney theme will that be fully compatible with Gutenberg?
ii) If the pages of the site using the Sydney free theme have been based on the text editor in the theme/wordpress rather than page builder, does that mean they will not appear correctly in future?
I guess that the Sydney them whether free or pro version may have a common underpinning so may be the answer to the Pro question applies but I need to understand if that guess is correct in the context of my two questions above.
Is the Sydney free theme fully compatible with Gutenberg?
If not? please explain what is likely to malfunction or act differently