Follow the instructions to create an FSE theme...
https://developer.wordpress.org/block-editor/tutorials/block-based-themes

Note: I've called the theme Fizzie since it sounds a bit like what you'd say if you quickly read out the letters F S E.
Where F = Full, S = Site and E = Editing.

Fizzie is/was the affectionate term for the Yamaha FS1E moped from the early 1970's.
It was a hybrid; more motorcycle than bicycle. It had pedals but you never rode it without starting the engine.

The Fizzie theme may also be considered to be a hybrid, with FSE template parts using server rendered shortcodes rather than native blocks. This is so I can implement the required functionality as quickly as possible.