This is a peer user community of tax preparers using Intuit's professional preparation programs. We are not Customer support or Technical support or even Intuit personnel. I understood what you asked, I did some research on your behalf, to better understand the issue. That's why I was comfortable providing that input. For instance, iOS is more in use in the arts, but I would never upload a MIDI file to a Tax site.

So, again, all I can do is point out that you would not upload Photos. I happen to know that a pdf is an Image File, which isn't the same as a Photo; it's more like OCR = optical character filetype that a programmer can code for. Also, I pointed out that tax format of txf (tax exchange format)  can be used by most tax programs as their import format standard. And that's the point; your HEIC is, per wikipedia:

"High Efficiency Image File Format is a container format for individual images and image sequences. The standard covers multimedia files that can also include other media streams, such as timed text, audio and video."

And that isn't an Office Work file for purposes of tax preparation. I also offered you what might be a simpler way to use your iPhone to generate photo files as pdf directly, addressing this comment you made:

"It's really annoying to have to print all these files to PDF."

Because you don't have to do that way.

I don't know what more we can do for you here. Sorry.