Due dates/times for tasks

You can try the Task List plugin, which enhances task-related features.

Task List plugin doesn't allow currently so set any due dates. So if you simply want a list of your scattered tasks there is an easy SiYuan-native solution for this by simply embedding an empty block and editing the SQL like this:

SELECT * FROM blocks 
WHERE markdown LIKE '%[ ]%' 
AND subtype = 't' 
AND type = 'i' 
ORDER BY created, sort

This will show you a list of all tasks found throughout your repository and lists them nicely in sorted order by creation date, i.e. the oldest task is the first one on the list. Once a task had been checked as completed it will be removed from that list when refreshing the embedded block.