TwinUI Default App Association
I'm not sure which Windows Update causes this issue but it changes the associations for a number of extensions causing quite the problem. A system restore failed and I was left to hunt for a solution. Searching around, I found a number of options but nothing solved the problem until I came across the following Powershell one-liner:
Get-AppXPackage | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}