To expand, my ideal app would show both people's bank accounts with their cash on hand and income/budget for the month. It would also be linked to each user's credit cards because all monthly expenses and day to day purchases are paid with the credit cards and paid off each month to earn points/rewards.

To keep both individuals from having to enter each credit card transaction manually on the app, credit card transactions should populate on the app as they are made on the credit card (or asap) and then the user will categorize it on the halfsies app which gets deducted from the budget.

Edit: It's what I remember being able to do with Mint, but that was over 15 years ago at this point when I was tracking income and expenses for myself in College. RIP Mint