The nuget.org feed is present. I ended up doing a workaround.
I got this from the fusion logs:
*** Assembly Binder Log Entry (25/06/2020 @ 11:00:48 am) ***
The operation failed.
Bind result: hr = 0x80070002. The system cannot find the file specified.
Assembly manager loaded from: C:\Windows\Microsoft.NET\Framework\v4.0.30319\clr.dll
Running under executable C:\Users\Owner\AppData\Local\UiPath\app-20.6.0-beta0093\UiPath.Executor.exe
--- A detailed error log follows.
=== Pre-bind state information ===
LOG: DisplayName = Microsoft.Identity.Client, Version=2.7.1.0, Culture=neutral, PublicKeyToken=0a613f4dd989e8ae
(Fully-specified)
LOG: Appbase = file:///C:/Users/Owner/AppData/Local/UiPath/app-20.6.0-beta0093/
LOG: Initial PrivatePath = NULL
LOG: Dynamic Base = NULL
LOG: Cache Base = NULL
LOG: AppName = UiPath.Executor.exe
Calling assembly : UiPath.MicrosoftOffice365, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null.
===
LOG: This bind starts in LoadFrom load context.
WRN: Native image will not be probed in LoadFrom context. Native image will only be probed in default load context, like with Assembly.Load().
LOG: Using application configuration file: C:\Users\Owner\AppData\Local\UiPath\app-20.6.0-beta0093\UiPath.Executor.exe.Config
LOG: Using host configuration file:
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: Post-policy reference: Microsoft.Identity.Client, Version=2.7.1.0, Culture=neutral, PublicKeyToken=0a613f4dd989e8ae
LOG: GAC Lookup was unsuccessful.
LOG: Attempting download of new URL file:///C:/Users/Owner/AppData/Local/UiPath/app-20.6.0-beta0093/Microsoft.Identity.Client.DLL.
LOG: Attempting download of new URL file:///C:/Users/Owner/AppData/Local/UiPath/app-20.6.0-beta0093/Microsoft.Identity.Client/Microsoft.Identity.Client.DLL.
LOG: Attempting download of new URL file:///C:/Users/Owner/AppData/Local/UiPath/app-20.6.0-beta0093/Microsoft.Identity.Client.EXE.
LOG: Attempting download of new URL file:///C:/Users/Owner/AppData/Local/UiPath/app-20.6.0-beta0093/Microsoft.Identity.Client/Microsoft.Identity.Client.EXE.
LOG: Attempting download of new URL file:///C:/Users/Owner/.nuget/packages/uipath.microsoftoffice365.activities/1.3.0/lib/net461/Microsoft.Identity.Client.DLL.
LOG: Attempting download of new URL file:///C:/Users/Owner/.nuget/packages/uipath.microsoftoffice365.activities/1.3.0/lib/net461/Microsoft.Identity.Client/Microsoft.Identity.Client.DLL.
LOG: Attempting download of new URL file:///C:/Users/Owner/.nuget/packages/uipath.microsoftoffice365.activities/1.3.0/lib/net461/Microsoft.Identity.Client.EXE.
LOG: Attempting download of new URL file:///C:/Users/Owner/.nuget/packages/uipath.microsoftoffice365.activities/1.3.0/lib/net461/Microsoft.Identity.Client/Microsoft.Identity.Client.EXE.
LOG: All probing URLs attempted and failed.
So I manually downloaded Microsoft.Idenity.Client 2.7.1 from nuget.org and added it to C:/Users/Owner/AppData/Local/UiPath/app-20.6.0-beta0093
The activity is now working