Filter items for selection in a Sub-Table

I am wanting to know how to filter the list of items that can be added to a sub-table as shown in the image. I click on the down arrow (1) then select from the list (2). The list is just going to grow and grow as I add more items to the parent table.

What I’m trying to achieve.
I have a timesheet table and a tasks table. In each timesheet entry I have a many to many relationship with tasks table that is shown through the tasks sub-table. I have a one to many relationship in both timesheet entries and tasks to a projects table (one project per task and one project per timesheet entry). When selecting a new task to add to my timesheet entry I’d like it to be filtered so that the tasks shown for selection are only those whose project matches the project of the timesheet entry.

The idea is that I have a list of task for a project then I load up my day with the tasks I want to complete that day so I use it like a daily work planner. Any given task may end up stretching over multiple days and even weeks for that matter. So the tasks already exist I’m not necessarily creating them through the timesheet, although this is also an option.

Hello @Kent_Watson2 ,
What you are trying to do doesn’t sound too complicated to accomplish in Coda, but in order to help you, it would be a lot easier if you share a dummy document that shows your setup and relations.
It is almost impossible to give you guidance if you only share a screenprint - it doesn’t give us any insights in the structure of your other table(s), the relations, and the filters you might already have tried to setup.
The easiest way to create a dummy doc is to copy your actual doc, delete confidential data and/or delete pages that do not relate to this problem. Or build something from scratch that resembles your working doc.
It also helps if there is some (dummy) data in the doc, so we don’t have to guess about the purpose of your columns.
Greetings,
Joost

Thanks for your response @joost_mineur . The link to a replica of the doc is below

The Time SHeet table is the main table. I also have a parent table called tasks, and tasks is set as a sub-table in TIme Sheets. I’ll add tasks via the parent task table then decide which of those tasks I’m going to work on that day. I want the add existing task to the task sub-table to include filters such as only allow me to select tasks that belong to the same project as that on the time sheet, also don’t show task that are set as Done. To be clear these are not necessarily filters to be used to display tasks in the sub-table only filters to be used to select existing tasks to add to the sub-table. So for example I don’t want to be able to see or select existing tasks that are “Done” when adding the task to the sub-table, but once a task has been added to the sub-table and I change its status to “Done” I don’t want to see it be removed from the sub-table.