What is the exact version of Lightroom ?
What is the OS ?
Have you tried another catalog ?
The Quick collection isn't set as the Target collection, some other collection is set as the Target collection.
Right click on the Quick Collection and select Set as Target Collection.
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The collection with a [+] sign at the end of the name is the Target Collection where you are adding the images with the grey dot.
The Targeted Collection can be the "Quick Collection" that exists in the "Catalog" panel just under the "Navigator" panel, or a "Standard" collection in the collections panel.
Also quicker than pointing to the grey dot with the mouse- is the [B] key that 'bumps' an image, or many selected images, into the target collection.