Initial Review:  Before upgrading,  the dt.csproj had .NET7 and was throwing errors about end of support for .NET7 
E:\work\myDotnetCore\dt>upgrade-assistant
USAGE:
    upgrade-assistant [OPTIONS] <COMMAND>
EXAMPLES:
    upgrade-assistant upgrade <PROJECT_PATH>
    upgrade-assistant upgrade <PROJECT_PATH> --operation Inplace --targetFramework net6.0
    upgrade-assistant upgrade <PROJECT_PATH> --operation SideBySide --targetFramework LTS --destination <NEW_PROJECT_NAME_OR_PATH>
    upgrade-assistant analyze
    upgrade-assistant analyze <APPLICATION_PATH>
OPTIONS:
    -h, --help       Prints help information
    -v, --version    Prints version information
COMMANDS:
    upgrade    Upgrade project or its features. This command lets you pick upgrade options and guides through upgrade process
    analyze    Scan and analyze .NET applications source code and dependencies to identify upgrade complexity
I ran:
<em><strong>upgrade-assistant analyze E:\work\myDotnetCore\dt</strong></em>
which produced the following report: 
 
 Selected options
──────────────────────────────────────────────────────────
 Source project     E:\work\myDotnetCore\dt\dt.csproj
 Target framework   .NET 9.0 (Supported until May, 2026)
 Upgrade type       framework.inplace
 Steps
─────────────────────────────────────────────────────────────
 Source project / Upgrade type / Target framework / Upgrade
─────────────────────────────────────────────────────────────
We have gathered all required options and are ready to do the upgrade. Do you want to continue? [y/n] (y): y
Building project 'E:\work\myDotnetCore\dt\dt.csproj'...
Starting upgrade of selected nodes for dt.csproj...
Traits
        {Name=UA, Version=0.5.829.41291}
        UAExtensibleOperations
        CPS
        SdkStyleProject
        OutputTypeExe
        C#
        GenerateDocumentationFile
        RelativePathDerivedDefaultNamespace
        .NET
        UseFileGlobs
        DynamicDependentFile
        ConfigurableFileNesting
        DependenciesTree
        ProjectImportsTree
        LaunchProfiles
        NoGeneralDependentFileIcon
        ProjectPropertyInterception
        PackageReferences
        AssemblyReferences
        ProjectReferences
        WinRTReferences
        OutputGroups
        AllTargetOutputGroups
        VisualStudioWellKnownOutputGroups
        SingleFileGenerators
        DeclaredSourceItems
        UserSourceItems
        SupportAvailableItemName
        IntegratedConsoleDebugging
        DisableBuiltInDebuggerServices
        PersistDesignTimeDataOutOfProject
        COMReferences
        Publish
        FolderPublish
        AppServicePublish
        DataSourceWindow
        CSharp
        Managed
        ClassDesigner
        SharedProjectReferences
        ProjectPropertiesEditor
        SupportsComputeRunCommand
        CrossPlatformExecutable
        SupportsHotReload
        Pack
        NetSdkOCIImageBuild
        net7.0
        {TargetFramework=.NETCoreApp, 7.0}
        Cli
        Inplace
        FinalizeProjectDependenciesChanges
        WaitForRestore
        BuildTelemetry
        {Operation=framework}
        NeedsBuild
        ProjectBuild
        NeedsSourceProject
        ProjectUnloadReload
Properties
        CommandSettings = Project: E:\work\myDotnetCore\dt, OperationControllerId: , TargetFramework: , Destination: , Template=, Config: , NonInteractive=False
        TelemetryEvent = Microsoft.UpgradeAssistant.Services.TelemetryEvent
        SourceProjectPath = E:\work\myDotnetCore\dt\dt.csproj
        SourceProject = dt (E:\work\myDotnetCore\dt\dt.csproj)
        OriginalTraits_E:\work\myDotnetCore\dt\dt.csproj = Microsoft.UpgradeAssistant.Traits.TraitsSet
        Traits = Microsoft.UpgradeAssistant.Traits.TraitsSet
        UpgradeType = framework.inplace
        Controller = Microsoft.UpgradeAssistant.Cli.Slices.Operations.Controllers.Framework.ProjectFrameworkInplaceController
        OperationDefinition = Microsoft.UpgradeAssistant.Operations.OperationDefinition
        TargetFramework = .NET, 9.0
        TargetFrameworkName = .NET 9.0 [grey](Supported until May, 2026)[/]
        EnvironmentVariablesKey = System.Collections.Generic.Dictionary`2[System.String,System.String]
        InitialDiagnosticsKey = ProjectBuildResult { Success = True, Diagnostics = (1) }
        CorrelationIdKey = 494fef4f-6f89-4df6-aadd-969a290dcb29
        Nodes = System.Linq.Enumerable+OrderedIterator`2[Microsoft.UpgradeAssistant.SliceNode,System.Int32]
        OperationTelemetryEventKey = Microsoft.UpgradeAssistant.Services.TelemetryEvent
Initializing operation...
Building project 'E:\work\myDotnetCore\dt\dt.csproj'...
project dt.csproj...
        Microsoft.UpgradeAssistant.Msbuild.Transformers.InplaceDuplicatePackageReferenceTransformer
        info: Done
        Microsoft.UpgradeAssistant.Transformers.TargetFrameworkTransformer
        info: Setting property 'TargetFramework' to 'net9.0' for project 'dt (E:\work\myDotnetCore\dt\dt.csproj)'.
        info: Done
Succeeded
dependencies.finalizer Finalize project dependencies...
        Microsoft.UpgradeAssistant.Msbuild.Transformers.ProjectDependenciesFinalizerTransformer
        info: Done
        Microsoft.UpgradeAssistant.Cli.Slices.Transformers.Project.BuildProjectTransformer
Building project 'E:\work\myDotnetCore\dt\dt.csproj'...
        info: Done
        Microsoft.UpgradeAssistant.Cli.Slices.Transformers.Project.ReloadProjectTransformer
        info: Reloading project...
        info: Done
Succeeded
file Dockerfile...
Skipped
file.1 get_dt-0.0.1...
Skipped
file.cs Program.cs...
        Microsoft.UpgradeAssistant.Transformers.Code.CSharp.DefaultAttributeTypeMapTransformer
        info: Done
        Microsoft.UpgradeAssistant.Transformers.Code.CSharp.DefaultMemberMapTransformer
        info: Done
        Microsoft.UpgradeAssistant.Transformers.Code.CSharp.DefaultNamespaceMapTransformer
        info: Done
        Microsoft.UpgradeAssistant.Transformers.Code.CSharp.DefaultTypeMapTransformer
        info: Done
        Microsoft.UpgradeAssistant.Transformers.Code.CSharp.DefaultTypeMapUsingsTransformer
        info: Done
Skipped
file.md README.md...
Skipped
Finalizing operation...
Building project 'E:\work\myDotnetCore\dt\dt.csproj'...
<strong>Complete: 2 succeeded, 0 failed, 4 skipped.</strong> 
It’s now working without the warning messages and upgraded to .NET9