An existing ACF site can move to Leiho Collections one content type at a time. In Leiho → Collections, an ACF type has Import into Leiho (administrators):

Preview: every ACF field group attached to the type, what each field becomes in Leiho (text → Text, repeater → List, flexible_content → Blocks, relationship → Reference…), and what doesn't carry over (fields without an equivalent such as page_link, taxonomy or user, conditional logic, default values, media restrictions, location rules other than the content type, ACF Pro repeater options), with the number of entries, fields and stored values.
Import: Leiho creates the collection with the same API names (camelCase and hyphenated names included), then copies the entries in batches through the editor's validation, with a progress bar. A refused value doesn't stop the import: it is listed with a link to the entry. Each entry is then checked: the JSON Leiho serves is compared, field by field, with what ACF served, and any difference is listed.
The type is now served by Leiho: /export, /content and /types give the same JSON as before (media objects, references, repeater rows, _layout of blocks, rendered rich text, choices, dates, numbers, booleans), and the visual editor's dotted paths keep working. The ACF field groups stay in place but no longer apply to this type.
Go back to ACF (in the collection's settings) serves the ACF values again and deletes the Leiho table of the collection.

Nothing is ever deleted from ACF: no postmeta, no field group, no post type. Values edited in Leiho after the import are not written back to ACF; going back restores the values of the import day. A content type registered by the theme or a plugin stays registered there (Leiho only takes over its fields); one declared in ACF's Post Types screen is registered by Leiho with the same settings if ACF is deactivated. Pages and posts can't become collections: their ACF fields stay in ACF.

Import from ACF