Hi @FredTheShred,
Could you please share a screenshot of your flow's configuration?
Is the Description column a Multiple lines of text type column in your Original list?
Further, do you want to insert the Description value from the Original list into another list as a plain text?
I suppose that the Description column is a Multiple lines of text type column in your Original list, is it true? If you want to insert the Description value from the Original list into another list as a plain text, I think the "Html to text" action could achieve your needs.
I have created two SharePoint lists on my side and the data structure of them as below:

Note: The Description column is a Multiple lines of text type column in my OriginalList, the Destination_Description column is a Single line of text type column in my DestinationList.
I have made a test on my side and please take a try with the following workaround:
The flow works successfully as below:

Please check and see if the following article would help in your scenario:
https://powerusers.microsoft.com/t5/Using-Flows/Send-an-email-when-a-new-item-is-created-in-SharePoint/m-p/112617/highlight/true#M2958
Best regards,
Kris