Images not displaying in text messages (show as HEIC, cannot be downloaded)

Like the issue reported in Photos not showing in messages. (SMS) - Apple Community, I cannot see images sent to me in text messages (group chat or individual chat). I see a grey box with the image file name and extension, but no photo. When I click on it, the image does not download. iMessage is on, MMS is on, iCloud photos is on, and all suggested solutions in the original thread were tried and failed. Any advice would be much appreciated. I'd like to see images as I did before updating to the latest iOS. Thank you!