Re: 8.0.18 A null was returned after calling the 'GetService' method on a store provider instance of type 'MySql.Data.MySqlClient.MySqlClientFactory'.

[Massimiliano Mattei]

Same issue here. I'm with 8.0.20 connector.
All three libraries are referenced in the project:
MySql.Data.dll
MySql.Data.EntityFramework.dll
MySql.Web.dll

In the web config I have

<entityFramework>
<providers>
<provider invariantName="MySql.Data.MySqlClient" type="MySql.Data.MySqlClient.MySqlProviderServices, MySql.Data.EntityFramework" />
</providers>
<defaultConnectionFactory type="MySql.Data.MySqlClient.MySqlProviderServices, MySql.Data.EntityFramework" />
</entityFramework>

But when accessing the provider from a webforms like this:

<asp:EntityDataSource ID="LogTypesDataSource" EntitySetName="eva_logtypes" Select="it.[LogTypeId], it.[LogName]" DefaultContainerName="MyDb" ConnectionString="name=ConnStringName" runat="server" />

I got the exact same error.
Visual Studio 2019. Asp.net 4.7.2