I got a new iPhone recently, and getting the photos off of it onto my PC in a way in which Lightroom could import them was a painful experience to say the least. There are a few settings on the iPhone now which cause the photos to be stored in a new HEIC format from Apple, instead of plain old JPEG. When connecting my iPhone to my Windows PC I had all sorts of issues with the PC even recognizing the phone as a storage device. To do so I had to turn off the automatic conversion of photos from HEIC while copying to the PC, and also disable the automatic compression to HEIC entirely, and turn off some iCloud settings.
EVENTUALLY I ended up with all the HEIC photos from my phone on my PC and I needed a way to convert them to JPEG en masse so I could get them into my old version of Lightroom. I used a program called Converseen for the batch conversion. I was a little wary of it at first because it looked like one of those shady websites which trick you into downloading crap and often show up high on Google results. However the software worked great and didn’t install anything untoward. I just had to add the HEIC images and I could select an output format and destination, and the whole thing converted fine.
And that was it! The conversion took a little while but I was left with good old JPEG files.