What she's saying is more like 'comfTERble', but she's putting too much stress on the 'ter'. It isn't natural. The TV and movie clips are ( of course) correct examples of a natural US pronunciation: three syllables with the stress on the first syllable. Here's the dictionary transcription /ˈkʌmf(ə)təb(ə)l/ - note the stress mark on the first syllable ˈkʌm. Interesting, she says 'comfortable' fairly naturally before the clips. But then when she repeats them after the clips, she is over-emphasising the second syllable. She seems to be a non-native speaker who learnt English at a young age, as she admits that she still occasionally struggles with pronunciation. Listen to how she says 'accurately' with too much stress on the full form 'ate' - that sounds very unnatural. I wouldn't use her as a speech model, if I were you. If you want a good pronunciation video for American English, you should follow Rachel's English. She gives the correct pronunciation here: https://www.youtube.com/watch?v=XWNySmK01fg

In the UK a lot of people certainly do pronounce it with -er-.

Yes, native speakers in the USA at least will use the variant. But if you are just having a conversation the variant naturally comes out as you are not enunciating each sound.

I live in NY and most people pronounce it,without the er sound, but it is good either way. ER sounds like OR when you say it quickly.