@julie67 , Oh no, a collapsed lung can be difficult to work through. I'm glad that they recognized the situation and admitted you. As @pb50 noted, areas on PET scans can light up for several reasons. It basically means that your body is 'active' in that area; it can be an infection, fungal, cancer, COVID, inflammation, etc. The level of 'uptake', or the amount that the area lights up (super bright or just slightly), may help to guide your doctor in the next steps.
The doctors from my first bronchoscopy (of lymph fluid) told my husband that I had cancer before I was even awake. So, be thankful that it's not obviously cancer.
A bronchoscopy three years later didn't show cancer, but the PET was dimly lighting up. Eventually they determined that I had a lung fungus. Not cancer.
Your doctors have seen enough to determine that they want to do surgery to get a better look at the tissue once it's removed. It's an overwhelming time for you, that's completely understandable and normal. What type of surgery are you scheduled for, wedge resection, lobectomy? Are you comfortable with your team and the plan?

My PET lit up "mildly avid" and my docs, 2 surgeons, pulmo, and radiologist all thought it was cancer with mets and it was not. It was hamartomas. They did a wedge resection and took some mediastinal lymph nodes anyway. My BIODESIX, Nodify Lung, test came back 12% chance of cancer. So It was correct. Not cancer.