HEIC is a container; HEIF is a container format. I don't know why images from my iPhone get saved with a HEIC extension... seems like it should be HEIF.
That said, when I move photos from my phone to by desktop via Signal; somewhere along the way it gets converted to JPEG so it's not a concern.
You do know that something similar is true for JPEG, right? :)
JPEG is a compression method. Files with JPEG-compressed data are most likely to be in either JFIF or EXIF container formats. Both will almost always use the .jpg/.jpeg file extension.
That said, when I move photos from my phone to by desktop via Signal; somewhere along the way it gets converted to JPEG so it's not a concern.