Query Loop Block: Add support for post_parent (Only show child pages)

[tzugen]

What problem does this address?

I thing that I encounter frequently is the need to list or preview the child pages of the currently viewed parent page.
This is currently not really possible with the Query Loop Block.
I found a workaround (assigning the child pages a new author, in order to be able to filter them) but thats not really nice.

What is your proposed solution?

Variant A:
A checkbox "Show only subpages". If checked, the query loop block will show only pages where post_parent == ID

Variant B:
A selector "Only show subpages of" which allows to pick one or more parent pages, from which to list the subpages.

[carlomanf]

#31272 is closely related.

[bradhogan]

Hey all. Any updates on this feature? This is heavily utilized in themes we create for online course creators who only want to show top-level "courses" on their courses archive page (and not all of the lessons / child posts within the courses CPT). We can't really update our themes to a full site editing theme until this is put back in place in the query block (roughly 1k users of our theme). Thanks all! Loving the direction Gutenberg is heading.

[paaljoachim]

Perhaps @ntsekouras Nik might have some feedback here.

[carlomanf]

Variant A: A checkbox "Show only subpages". If checked, the query loop block will show only pages where post_parent == ID

Variant B: A selector "Only show subpages of" which allows to pick one or more parent pages, from which to list the subpages.

I see that #40933 is an implementation of variant B as described by the issue author. I welcome it, but I would also welcome Variant A as a separate implementation, as they serve slightly different purposes. #31272 and #39192 are a little bit more relevant for the purpose of variant A, if I am reading it correctly.