The plan forecast page is only available on the desktop web app at https://app.monarchmoney.com/plan?timeframe=monthly
This view is similar to the monthly Plan Budget page but it shows all 12-months of the current year in a grid so you can quickly edit multiple monthly budgets across all categories.
This can be particularly helpful if you want to enter a known future expense such as a big vacation, a large bill or seasonal expenses like holiday gifts or taxes.
You can also switch the view from monthly to yearly:
The yearly view show 10 years in 1-year intervals. Yearly budgets are just the sum of all 12 monthly budgets so you won't be able edit the total yearly budget but if you edit a monthly budget inside that year it will change the yearly amount.