If you are looking for the Exchange API to configure modern authentication for Veeam, you’ll find that it is no longer present under “Request API Permissions” -> “Microsoft API”.
Instead, what you want to do is go into “APIs my organization uses” under the “Request API Permissions”, then search for “Office 365 Exchange Online“.
It’s basically the same thing, only a bit harder to find, as the search doesn’t show up results if you look for “Exchange”.