Hi @Vanessa ,
Thank you for posting in this community.
It seems this is not a common issue per my test. Immediately displayed in the properties panel after being added.
Check if the same issue occurs with other SharePoint site collections.
But I found a workaround, you need to customize description column using Power Apps. In your document library (External links), click on Power Apps>Customize forms>it will open Power Apps windows> then Click on +Add field and select the default description column to add. See image below for your reference(Here's an example of the description column):
After add description column there click on File>save, after save click on publish to SharePoint, then go to SharePoint online document library, select the link file and in properties menu click on Edit all to add your description.
I hope this works for you.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.