Google Sheets App Script improvements and restricted access

Currently we a Google sheets document that has the following tabs
Task Manager - this is the tab where all task are listed for all employees.
TCM - Employee Alan
PTL - Employee Gameel
Bookkeeping - Employee Sarah

When a row on the Task Manager tab is completed with details, it automatically duplicates the row to all the other sheets.
Column C on all sheets is where the employee name is inputted. This column has a filter so the individual employee can filter the rows to only show the tasks that apply to their name.
When an employee makes changes to any cell in the row on the other tabs the edits are updated in the Task Manager tab also. Two way sync. From Task Manager tab to other tabs and back to Task Manager tab.
The filters are also re applied on edit in the App Script.
The App Script currently does all this but the syc is a bit slow. and we need to hide the tasks and tabs that do not apply to specific employees. Only specific shared employees can view the entire document.

This is what we require the sheet to do..
Update all tasks for all employees on Task Master tab
Based on employee name the task is duplicated on a specific extra tab.
Any edits sync to and from the Task Master tab
Any filters are remembered (if they are require)
Faster syncing

There could be a better way to achieve this by replacing the current App Script but we also require...
Shared access to specific employees gives access only to their specific tab - basically they cannot view Task Manager tab or any other tab or filter other than the tab they have been granted access to.
Also the dates need to be a day picker style, currently this does not filter over on all sheets when programmed on the Task Manager tab.
Current sheet and App Script attached if required