There are three users. When one user changes the period for the profit and loss account on the summary page, it gets changed for all other users.
Example:
User 1 changes the period to show profit and loss account balances from 1 January 2019 to today.
User 2 changes the period to show profit and loss account balances from 1 August 2019 to today.
When user 1 logs back on his machine the summary page is showing balance from 1 Augst to today.
Is it possible for the Manager to NOT change the specified period based on the changes done by other users?
No. The multi-user capability only allows access for multiple users. It does not allow them to separately define accounting variables in the database. User permissions control what actions users may take and what they can view. But those do not involve changing accounting variables. Just as users cannot view separate Summary date ranges, a bank account cannot have one balance for one user and different balance for another.
You might ask why, then, users can individually determine language preferences. That is because language does not involve database variables. Language translations occur as a lookup process as labels are being displayed. No accounting variables are involved.