Clarification on media assigned to post

Don’t know if it’s the right section to post, I hope it is.

I’m using Elementor page builder on a website, and I use the Image Gallery Block to show all the images uploaded in a post as a gallery. The gallery shows fine.

Usually I upload the images in the body of the post: I edit the post, click on “Add Media”, drag-n-drop my images and I’m done.
If I go to Media, in the column “Uploaded to”, I see that the images appear uploaded to my post.

Now, the problem is that I would like to use a custom field to upload my images, for various reasons.
I created a custom field using the Toolset Types plugin, uploaded my images but the gallery is empty.
If I click on “Add Media”, in the post edit page, I don’t see any image.
The problem is that if I go to Media, in the column “Uploaded to”, the images actually seems to be uploaded to my post.

Why my images do not appear in the post edit page but appears in the Media section, “Uploaded to” my post? Is this an intended behaviour? Are those two different things? How could I “attach” the images to my post so that they appear in the gallery?

I don’t think I’ll have any problem on coding something custom if needed