Prior Reconciliations way off (MAC)

@paul@f  First, Quicken management doesn't read these posts. If you want to add your vote for a reconciliation report, please click here to visit the Idea thread for this feature and add your vote in favor of it. (In the yellow box under the first post, click the little arrow under the vote counter.)

Next, are you using version 6.11 or 6.2? (There's a slight change in the reconciliation screen between the two; one of the changes is that the prior balance is not shown and doesn't need to be entered in 6.2 -- but that isn't the source of your problem.)

Are your problems with one account or with multiple accounts?

If you click on one of the problematic account and select Accounts>Reconciliation History, does it show one or more prior reconciliations with a discrepancy? Please provide more information about what it shows.

Without seeing all your work, it's often hard to suggest exactly where to proceed when your reconciliation is off. It helps if you understand that Quicken is simply adding up all the debits and credits from the beginning of time to the start date of the reconciliation to come up with its starting balance. The "Quicken Balance" is the sum of every transaction, since the beginning of time, which is reconciled.

If your running account balance in Quicken is correct, but the reconciliation amount is not, that suggests to me that there's something in the past which may not be marked as reconciled; the transaction exists so the overall account balance is correct, but if it's not reconciled, it's not included in the starting balance. I'd either scroll through your account looking for any transactions without the green reconcile check-mark; save time by clicking on the Clr column to temporarily sort the register by status: all unreconciled together, all cleared but not reconciled (blue check-mark) together, and all reconciled together. (Don't forget to click back on the Date heading to restore the register to date order when you're done.) 

@Mary Jane Steward It's impossible to offer significant advice because you haven't provided any information. If you still have access to the Windows computer, I'd try to compare the account balance at various dates to zero in on where the discrepancy(ies) are coming from. Perhaps start with an "easy" account -- such as a credit card account with a low volume of transactions. Work your way up to your primary credit card or checking account. Compare balances as of the end of 2020, end of 2019, end of 2018, etc. If everything matches as of 12/31/19, but is off as of 12/31/20, then check the midpoint of 6/30/20. Keep cutting your interval in half until you zero in on the source of the discrepancy.