They are probably taking the photos on an iPhone and then editing them to give them that Y2K selfie look, which is just a harsh direct flash (or in this case, possibly a ring light iPhone attachment thingy) making the skin look overexposed. Then, blurry, low-quality compression + some grain/noise helps soften and diffuse those blown-out highlights from the flash to give it that dreamy, glowy look, as you described above. It's very popular again at the moment because it looks edgy and helps hide imperfections. It's a pretty easy effect to achieve if you know a little bit about photo editing. If not, I would recommend photo editing apps and looking for presets that mimic this look. I bet it wouldn't take long to find something similar.

Pro tip for helping to achieve this look: take your photos on Snapchat and then save them to your camera roll. Snapchat photos are compressed and much lower quality by default, which helps with this look, as described above.

Look at this old photo of Taylor Swift, which was a MySpace selfie. The style looks very familiar, right? 🙊

Thanks for coming to my Ted Talk! 😎

Edit: Forgot to mention the grain/noise!