I suspect Airport Utility will remain viable until it is no longer compatible with MacOS/iOS/iPadOS but it is no longer under development, and to the best of my knowledge it is no longer supported.
After thinking about what I said, I went back and looked up Apple's Policy on Vintage and Obsolete Products
products will be supported for five years after the product is no longer sold and seven years if parts are available
According to MacTracker the Airport Extreme 802.11ac and Time Capsule 802.11ac were dropped in April 2018 which means that they can be taken in for repair until April 2023, and after that, until April 2025 if parts are available
I wouldn't count on parts being available after April 2023 and I don't think
that also guarantees
Airport Utility will be compatible with Big Sur or its successors.