* SEE POST https://community.esri.com/t5/arcgis-pro-documents/recent-microsoft-net-update-resulting-in-arcgis/t... from ESRI community moderator KoryKramer for clearer guidance as of October 13, 2022. Thanks to Kory for the post.
We have resolved the issue at our organization by uninstalling Windows update KB5017262 (2022-09 Cumulative Update Preview for .NET Framework 3.5 and 4.8 for Windows 10 Version 21H2 for x64). Uninstalling an OS patch isn't ideal, but allows us to continue working in Pro 2.9x. Here's hoping ESRI releases a fix in short order!
UPDATE - Further to this issue, we tested on a machine running 2.9.3. We left KB5017262 in place and installed the latest .NET Framework (4.8.1) and the issue resolved. Thanks Daniel_Schmidt for bringing up .NET versions as an avenue to investigate.
UPDATE (September 29, 2022) - Yesterday we tested turning windows updates back on. .NET 4.8.1. KB5017266 has recreated the problem in our environment at Pro 2.9.2 and 2.9.3. (September 20, 2022-KB5017266 Cumulative Update Preview for .NET Framework 3.5 and 4.8.1 for Windows 10, version 20H2, Windows 10 Version 21H1, and Windows 10 Version 21H2).
UPDATE (October 3, 2022) - Our case supporter has found this report from Windows. KB5017266 and KB5017262 both have known issues. The report indicated these Windows Server Update Services (WSUS) updates are listing errors (should not have been released): https://support.microsoft.com/en-gb/topic/september-20-2022-kb5017266-cumulative-update-preview-for-...
This would affect users working in organizations where Windows updates are managed by WSUS and likely other types of update manager software.