I stucked with it for hours, the only way for me was:

Uninstall your MySql Connector

Remove MySql.Data from references

Remove MySql.Data.EF from references

Remove EntityFramework from references

Uninstall MySql.Data from Nuget packages

Uninstall Entity Framework by Microsoft from Nuget packages

Install Mysql Connector 6.9.12 from https://downloads.mysql.com/archives/c-net/

Install MySql.Data 6.9.12 from Nuget packages

Install Entity Framework by Microsoft 5.0.0.0 from Nuget packages

Add referencies: MySql.Data 6.9.12; MySql.Data.EF 6.9.12

In app.config you need this:

  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="EntityFramework" publicKeyToken="b77a5c561934e089" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-5.0.0.0" newVersion="5.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="MySql.Data" publicKeyToken="c5687fc88969c44d" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-6.9.12.0" newVersion="6.9.12.0" />
      </dependentAssembly>
    </assemblyBinding>
  </runtime>

In package.config you need this:

  <package id="EntityFramework" version="5.0.0" targetFramework="net461" />
  <package id="MySql.Data" version="6.9.12" targetFramework="net461" />

I'm not sure about it will work for you, but it worked for me when i've got the same error 2 days ago.