This is just a workaround in the absence of a file manager feature like you are describing:
Create one post (you can keep it as Unpublished) – I have one post named “Images” I use for this purpose – where you can upload and store all of your site’s images on that one post.
Then when you want to know the URL to use an image later on within another post, just go to that “Images” post and right-click on the image and select “Copy image address” to copy the URL. Then you can paste that URL into another post without uploading the same image again and creating an unwanted duplicate.
You can use the Gallery card as many time as you want on the same post (each gallery can contain 9 images.) This is the most compact display of the images.
You can also use the Image card, or the Markdown block which both allow you to select and upload images from your computer’s local drive.