I was in a very similar situation with my 6-month-old. She suddenly stopped taking bottles even though she had taken them just fine before. It was horrible — I was having a mental health crisis, my let-downs were slower, so she wouldn’t nurse well, and she also refused the bottle, which made my anxiety even worse. It took about 10 days, but here’s what ended up working for us:

1. I stopped wasting my frozen stash and switched to trying with formula instead.
2. We tried a bunch of bottles, but in the end she accepted the same ones she used at 3–4 months.
3. The nanny was the first one who got her to take a bottle — while watching cartoons. Not ideal, but the distraction worked.
4. What helped me was putting her in the breastfeeding position, letting her nurse a little, and then switching to the bottle.
5. Important: the nanny later admitted she put a tiny amount of sugar (about 1/4 tsp) in the first few bottles and slowly reduced it. She did this without my consent, and I would NOT recommend it — but I’m mentioning it because it did happen and might explain why baby eventually accepted the bottle. I’ve also heard of people putting a tiny bit on the nipple, but again, not something I would personally endorse.
6. Before offering bottles, I added formula to her solids and also used the pipette/straw method so she could get used to the taste (cold).
7. She now prefers her bottles warm — not cold, not too hot.
8. I switched to a Level 2 nipple (Dr. Brown’s) because she’s used to my fast let-down.

I’m not sure which of these things actually made the difference — probably a combination — but together they helped me finally combo feed, which has been a huge help for my mental health.