@Pallavi15
We have a similar case while migrating Legacy applications to .Net Framework 4.5 on Windows Server 2019. It worked in my case, however, please test the entire application on a test environment on Windows Server 2019 with .Net Framework 4.5.
Please refer the below links for more information on the same topic
Application compatibility in the .NET Framework:
https://learn.microsoft.com/en-us/dotnet/framework/migration-guide/application-compatibility
Version compatibility and Backward compatibility:
https://learn.microsoft.com/en-us/dotnet/framework/migration-guide/version-compatibility
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