@tutul07 Welcome to Microsoft Q&A forums and thank you for your interest in Azure services.
General availability of .NET 5 support for Azure Functions was announced on March 10 2021.
Please find the complete blog post here
You shouldn't have any problems upgrading your ESB app to .Net 5.0
Even if you have class libraries on different .Net versions, you will now be able to run them out of process.
More details are here
Do let us know if you have any specific questions.
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