My method has some manual steps that I have not yet automated, so I won’t go into all the specifics. But basically, I enter known future checking account transactions a month or two ahead directly into the Transactions sheet. When the actual transaction gets downloaded from the bank, I match it with the one I entered manually using the Reconcile community solution. This works extremely well.
To project future balances in my checking account, I use the Account Register community solution. It shows a checkbook-style register for selected accounts along with a running balance. This also works very well and lets me know if my account balance will go negative at some point in the future.
I make heavy use of conditional formatting in the Transactions and Account Register sheets to highlight future dates, manual transactions, and negative account balances in the register.
The manual part of my method involves a separate sheet that lists all my known recurring transactions (expenses and deposits). Currently I manually copy/paste them into the Transactions sheet, and update dates and amounts manually. I haven’t quite automated that part yet. There are some community solutions that seem to have similar functionality, but when I’ve looked at them there’s always something that doesn’t quite fit my mental model so I’m pursuing it my own way.