What approach should I take with dropdowns and select all option

I have multi-select dropdown with 3000 tasks loaded from a database. Many tasks can be assigned to a user and I want to have the option ‘Select all’, but the front end is the easy part.

My Laravel database structure is the following:
I have a table with all of the tasks and a table named user_has_task where I insert every assigned task of the user. Then I use global scopes to filter the tasks accessible by the user.

But the question is what approach should I use – I can insert all 3000 tasks as new records in the user_has_task (imagine having 100 users who all have access to every task, the table will become very big 100*3000 = 300000 records) or I could insert some specific single record that tells the code that this user has access to every task (but this way I will lose the ability to remove specific assigned tasks from the user (imagine assigning 3000 tasks but you want to removed 1 of the tasks from this user))