In reply to Gary Taylor.

Agreed; how to do 'X' in Gutenberg or FSE isn't clear in many cases in the documentation or I've found more often, there isn't an answer just yet.

I asked specifically how themes should migrate to the FSE this summer - https://github.com/WordPress/gutenberg/issues/24313 - and the answer is not yet known.

Generally, there's been more focus on making FSE themes from scratch.