And the answer is:

Add autoorient=true to the query string, or automatically to all image processor tasks like so:

public class ConfigureImageSharpMiddlewareOptionsComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
        => builder.Services.Configure<ImageSharpMiddlewareOptions>(options =>
        {
            // Capture existing task to not overwrite it
            var onParseCommandsAsync = options.OnParseCommandsAsync;
            options.OnParseCommandsAsync = async context =>
            {
                // Custom logic before
                context.Commands.Add("autoorient","true");

                await onParseCommandsAsync(context);

                // Custom logic after
            };
        });
}