EF Core “InvalidOperationException: Include has been used on non entity queryable” on IQueryable

I have the following schema:

public class Post {
    public string Id {get;set;}
    public string Content {get;set;}
    public AppUser AppUser {get;set;}
    public List<PostTag> PostTags {get;set;}
}

public class Tag {
    public string Id {get;set;}
    public string Name {get;set;}
    public List<PostTag> PostTags {get;set;}
}

public class PostTag
{
    public string PostId { get; set; }
    public Post Post { get; set; }

    public string TagId { get; set; }
    public Tag Tag { get; set; }
}

With the following db relationships:

builder.Entity<PostTag>()
    .HasKey(x => new { x.PostId, x.TagId });

builder.Entity<PostTag>()
    .HasOne(st => st.Post)
    .WithMany(s => s.PostTags)
    .HasForeignKey(st => st.PostId);

builder.Entity<PostTag>()
    .HasOne(st => st.Tag)
    .WithMany(s => s.PostTags)
    .HasForeignKey(st => st.TagId);

I'm writing a query to get all the Posts that are linked to a specific Tag, based on the provided TagId.

First I get all the posts using:

var postsQuery = _ctx.PostTag
                    .Include(st => st.Post)
                    .Where(st => st.TagId == {provided TagId})
                    .Select(st => st.Post);

Since I want to include some further data to each post, I do:

var postsWithExtraData = postsQuery
                            .Include(s => s.AppUser)
                            .Include(s => s.PostTags)
                            .ThenInclude(st => st.Tag)
                            .OrderByDescending(s => s.TotalVoteCount)
                            .ToListAsync();

But the query breaks on the first .Include with this error:

EF Core “InvalidOperationException: Include has been used on non entity queryable”

Why is this happening and how can I fix it?

EDIT: Potential solution that I got to work:

var posts = _ctx.PostTag
                    .Include(st => st.Post)
                    .ThenInclude(s => s.AppUser)
                    .Include(st => st.Post)
                    .ThenInclude(s => s.PostTags)
                    .ThenInclude(st => st.Tag)
                    .Where(st => st.TagId == request.TagId)
                    .Select(st => st.Post)
                    .ToList();

Would love to know if this is a good approach or not.