Two salaries can create more income and more complexity.
One person pays the mortgage. The other covers childcare, groceries and the stream of smaller family costs. Both feel they are paying for everything. Neither can see the whole household picture.
The problem may be visibility, not spending
Separate accounts are not a problem by themselves. The problem is when the household has no shared view of income, fixed costs, debt, insurance, pensions and savings.
A monthly 20-minute household money meeting can do more than another budgeting app if it makes the full picture visible to both people.