For federal taxes and most states, the deadline for filing an extension for your 2020 taxes was May 17, 2021. So if you filed for an extension after that date, disapproval of the request is pretty much a given. when you do file the 2020 tax return you can expect to be assessed interest on any taxes due. There's the prossibility of being assessed a late filing penalty too.
Generally, if you are due a refund then no interest, penalties or late filing fines are assessed.
