After installing update Revit 21.1.10.26 (21.1.1 Hotfix) https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2021/ENU/RevitReleaseNotes/files/2021updates/RevitReleaseNotes-2021updates-2021-1-1-html-html.html) we have seen that the registry sometimes get a corrupt value on the Install location.
Check the HKLM registry under the SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\{7346B4A0-2100-0510-0000-705C0D862004} key and the "InstallLocation" value. It should say something like "C:\ProgramFiles\Autodesk\Revit2021\".
If it only says "Revit 2021\", it means that the Autodesk's upgrade has not been done correct.
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