OK, so your main tasks are note files, and in your current you’ve got links to these files which if present you want removed from the global list.
Firstly, in order to do any filtering on the tasks links from any given section in the current file we need to do the following magic:
FLATTEN
list(
filter(
this.file.tasks,
(t) => meta(t.section).subpath = "PO Tasks"
)) as PO_Tasks
This does the following:
FLATTEN ... as PO_Tasks
– Whatever expression follows the “…”, is stored into PO_Tasks
for subsequent handling
list( ... )
– The next expression will be treted as a list (and not expanded into its separate items as is the default for FLATTEN
)
filter( this.file.tasks, (t) => ... )
– The filter()
function will return any elements of the list is given (aka this.file.tasks
) where each element, t
, is matched against the next expression
meta(t.section).subpath = "PO Tasks"
– From a given task, we lift out the section
link, and using meta()
we look at its components, and in particular the subpath
element which holds the actual heading text
So all in all, this rather lengthy snippet pulls out the list of tasks that are in the “PO Tasks” section of the current file.
But you didn’t want that list, but to exclude all links from that list to be excluded from the overall list of files matching your query, and that is achieved by doing:
WHERE !contains(PO_Tasks.outlinks, file.link)
We don’t want to include any file
’s link which matches any links in the prioritised task list.
Using both of these we’ll end with the following query:
```dataview
TABLE due-date as "Due"
FROM (#task or #exam) and #obsidian_forum_example
FLATTEN list( filter( this.file.tasks, (t) => meta(t.section).subpath = "PO Tasks" )) as PO_Tasks
WHERE !contains(PO_Tasks.outlinks, file.link)
WHERE complete = "no"
SORT due-date ASC
LIMIT 10
```
Hopefully that should work according to your specifications! 
Bonus tip: How to present code properly in a forum post
If you want to showcase either markdown, or code blocks, or dataview queries properly in a forum post, be sure to add one line before and one life after what you want to present with four backticks, ````
. This will ensure that any other backticks (like for code blocks or queries) is properly shown.