@brett @goodmanjosephd I don’t know if you have tried it yet, but the Savings Budget sheet is an enhanced version of the original Envelope template that is compatible with Foundation template solutions. One key ability is to be able to individually set categories on the Categories sheet as Savings under the Track column. This will allow any unspent or overspent dollars in that category to roll over to the next period. There is a drop-down on the Savings Budget sheet in G6 that you can toggle the adjust column to add to Savings, rather than budget. Note that you may need to set the current period budget to $0 for it to show on the sheet. Savings adjustments are logged on the Budget Journal sheet. As a word of caution, unlike budget allocation, there is no error checking to ensure savings adjustments are using dollars that are actually available. This flexibility, however, is what allows you to be able to seed a savings goal that is already in progress prior to the starting period on your sheet.
I highly recommend trying out the Savings Budget sheet and see if it can meet your needs. There is a migration tool you can use to migrate your data from the Envelope Budget template outlined on the page I linked above.