When DOTNET_MULTILEVEL_LOOKUP is set to 0, .NET ignores any globally installed .NET version. Remove that environment setting to let .NET consider the default global install location when selecting the best framework for running the application. The default is typically C:\Program Files\dotnet, which is where the installers install .NET.
https://docs.microsoft.com/en-us/dotnet/core/install/windows?tabs=net50#download-and-manually-install