Thank Gile.
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Relating the Migration guide, I've found some pieces of information from Autodesk Civil 3D 2025:
Known Issues in Civil 3D .NET Core Development
https://help.autodesk.com/view/CIV3D/2025/ENU/?guid=GUID-B50CC834-E202-48FE-9C64-526EF9828535
"....
Plugin fails to load due to the lack of a framework reference to Microsoft.AspNetCore.App
Civil 3D does not rely on Microsoft.AspNetCore.App, so it has not added this reference. If your plugin has a dependency on it, it may prevent the plugin from running.
Solution: Edit the acdbmgd.runtimeconfig.json file located in the Civil 3D root folder by adding a reference to Microsoft.AspNetCore.App. If you are using a script or installer to add it, incorporate logic to check whether the user or other plugins have already included it before adding it to avoid duplication. Also, ensure that the desired version has been installed by Civil 3D using the "dotnet --list-runtimes" command. Otherwise, you may consider including the framework installer within your plugin installer. ..."
About Civil 3D .NET Core Development
https://help.autodesk.com/view/CIV3D/2025/ENU/?guid=GUID-E6657034-71E5-4753-8AFD-139DC612B86D
.....As per claims such as https://github.com/dotnet/runtime/issues/68041, .NET framework DLLs could continue to work within .NET Core runtime as long as they don't use any API exclusive to .NET Framework, However, you should conduct thorough testing on your own to ensure it functions properly within the .NET Core environment if you choose to stay with .NET framework." ....
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I wonder why those information does not appear in AutoCAD 2025 ".NET migration guide"
https://help.autodesk.com/view/OARX/2025/ENU/?guid=OARX-ManagedRefGuide-_NET_Migration_Guide
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Previously, I've tested my .NET Framework 4.8 libraries in AutoCAD 2025 (by mistake). My project is multi targets and I load the wrong file. It works so smoothly that I didn't find that the wrong version is loaded, until I found commands under #If NET5_0_OR_GREATER directive do not work as expected.
However, another guy in feedback forum (Alexandr Chernishev) reported that his plugin could launch, work, then the error “SQLClient file not found” popped up.