Hyperlink attachments in ArcGIS Online
If you are looking to add an image from attachments:
Here you can see I have added 2 attachments to my record.
Here, I have added an attachment viewer using +Add Content in the pop-up.
This way shows multiple images at a time in the pop-up.
You can add text and other content types to the pop-up along with your attachments.
You should see the attachments in the table when you look at the data view of your layer.
If you are looking to add a hosted image from a URL:
You would add a field {Link1} in your table and add links to each record as text "https://yoursite.com/your-image123"
You can add as many fields as you have images. So if you want 3 images per record, add 3 fields {Link1} {Link2} {Link3}
Then add an image content type to the pop-up using +Add Content.
In the URL field click the {} and add your field.
Then add another image content block for Link 2 and another for Link 3.
This way shows only one image at a time in the pop-up.
Add Attachments (Data Management Tools)
Configure and manage attachments on hosted feature layers
Let me know if this is the workflow you are looking for.
