Steps to reproduce the issue

With J4 sample data
Creat a 'Test child' of the 'New feature: Workflows' menu item in the Main blog menu
Open Breadcrumbs Module for edit
Navigated to Menu Assignment tab
Select 'Only pages selected'.
The 'Test child' was displayed at the bottom of the list instead of in the tree under the 'New feature: Workflows' menu item

Expected result

The 'Test child' menu item should be displayed in the tree under the 'New feature: Workflows' menu item

Actual result

The 'Test child' menu item is displayed at the bottom of the list

System information (as much as possible)

Additional comments

Problem also exists for the 'All pages except those selected' tab

https://forum.joomla.org/viewtopic.php?f=808&t=1001819