Hi there
It seems that we don't have documentation for how to do this with the current blocks-based UI, so let me describe what is involved.
(For reference, the documentation for the legacy interface is: https://toolset.com/documentation/legacy-features/views-plugin/displaying-brother-pages/.)
Assuming the starting point is a template to show the child posts (where you want to show other posts that are children of the same parent, i.e. siblings), you need to insert a another content template which you trick into thinking that the current context is the parent post, and to that template you add a View to display its child posts (minus the currently displayed child post).
I set this up on a sandbox site so that you could see the implementation. You can access the admin pages via this link: hidden link
I created post types Projects (parent) and Tasks (children), with some sample data.
There is a Content Template to display single Tasks.
There is another Content Template which is not assigned to any post type which contains the View to display child posts, and this Content Template gets added to the first template for tasks.
The context for the template needs to be set to the parent Project post for this to work.
It's only possible to do that by inserting the template via shortcode (there is a Content Template block that doesn't allow for switching context), so you will see that is done with a shortcode like so:
[wpv-post-body view_template="project-context" item="@project-task.parent"]
The view_template attribute is the slug of the template, while the item attribute is used to set the context to the parent post of the project-task relationship. (The Toolset Shortcodes link in the admin toolbar lets you generate such shortcodes rather than having to remember them; choose to insert a Content Template and for the Posts Selection specify the relationship as required.)
The final piece is that the View, which displays tasks, needs to only display tasks of the "current" project rather than all tasks, and so in the Content Selection settings for the View block, you need to add a post relationship Query Filter to show posts related to the current post in the Projects-Tasks relationship.
The setting not to include the current page in the results means that only sibling tasks are shown and the current task isn't repeated.
Take a look and let me know if you run into problems.
