BizTalk 2020 WCF-OracleDB adapter Error

If you changed BTSNTSvc.exe.config / BTSNTSvc64.exe.config files, you may also need to change MMC.exe.config (BizTalk admin console) for BizTalk admin console. You may also need to change the Oracle.DataAccess.Client to point to newer version (see below).

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https://docs.microsoft.com/en-us/biztalk/adapters-and-accelerators/post-installation-steps-for-biztalk-adapter-pack-2016#use-a-newer-oracledataaccessdll-version
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<dependentAssembly>
<publisherPolicy apply="no" />
<assemblyIdentity name="Oracle.DataAccess" publicKeyToken="89b483f429c47342" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-65535.65535.65535.65535" newVersion="4.122.19.1" />
<!--<bindingRedirect oldVersion="0.0.0.0-65535.65535.65535.65535" newVersion="4.122.18.3" /> -->
</dependentAssembly>
</assemblyBinding>
</runtime>

<system.data>
<DbProviderFactories>
<add name="Oracle Data Provider for .NET" invariant="Oracle.DataAccess.Client" description="Oracle Data Provider for .NET" type="Oracle.DataAccess.Client.OracleClientFactory, Oracle.DataAccess, Version=4.122.19.1, Culture=neutral, PublicKeyToken=89b483f429c47342" />
<!--<add name="Oracle Data Provider for .NET" invariant="Oracle.DataAccess.Client" description="Oracle Data Provider for .NET" type="Oracle.DataAccess.Client.OracleClientFactory, Oracle.DataAccess, Version=4.122.18.3, Culture=neutral, PublicKeyToken=89b483f429c47342" />-->
</DbProviderFactories>
</system.data>
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I would also make sure to update to the latest BizTalk 2020 CU (CU2 currently) as there were some updates related to Oracle adapter after initial RTM release.

I hope this helps.