I'm not sure what "All attempts..." included, but OData has its own method for configuring casing. The default is Pascalcase, but most people expect Camelcase as the de facto for JSON, which is also the default for ASP.NET Core. API Versioning aligns to Camelcase by default as part of the 80/20 rule with the intent you have less to configure.

Reverting to the default settings is as simple as:

builder.Services.AddControllers().AddOData();
builder.Services.AddApiVersioning()
 .AddOData(
 options =>
 {
 // the default factory method includes .EnableLowerCamelCase()
 options.ModelBuilder.ModelBuilderFactory = () => new ODataConventionModelBuilder();
 options.AddRouteComponents();
 }); 

The Versioned OData Model Builder topic provides additional documentation and the builder is exposed via ODataApiVersioningOptions.ModelBuilder.