No longer able to import HEIC photos from iPhone using the Photos.app on High Sierra

I run High Sierra on my old Mac. Importing pictures from my iPhone running 15.7.2 was never a problem. Roughly since December 2022, I haven't been able to import photos. The error message is always the same: Unable to import due to unknown format. The pictures are in HEIC and I have HEIC pictures on my Mac from previous imports and I can still open these. My Mac knows the format, but the Photos.app somehow has stopped recognizing it. Perhaps it's a deeper problem and the format is just "an excuse" but the app is now unable to import anything?