On the mobile app, in the Budget tab, the currency symbol for Overview totals and Available totals changes based on the 'Default Currency' setting. Only the currency symbol changes, not the amounts.
Also, in the Inflow and Outflow tables, if you don't have a 'Default Currency' selected, then it displays the currency symbol of the 'Budgeted' amount in the 'Activity' and 'Available' columns, even though the amount value displayed in those columns is in another currency (the Primary Currency).
The currency symbol should be based on the primary currency of the budgeting accounts, not the 'Default Currency' in the app.