New Linux box, old home directory.
Attempting to execute dotnet ef database update repeatedly failed with the error, “The framework ‘Microsoft.NETCore.App’, version ‘6.0.0’ was not found.” Individual dotnet commands (dotnet --version, dotnet build, etc) were working, which became very confusing.
Google was not my friend today, the error as a search term produced lots of noise, some issues from github that indicated old bugs, and red herrings.
I finally stumbled across the problem: the value of the environmental variable DOTNET_ROOT was wrong. The value was /opt/dotnet-sdk-bin-5.0, but the installed version was 6.0.
Version 5.0 had been installed initially, but I upgraded it during the same login session. While /etc/env.d/90dotnet-sdk-bin-6.0 was installed properly, and used the correct value, it would not take effect until I logged out and/or rebooted.
Shame on Microsoft for their terrible, uninformative errors.