@constantinos
I am five years out, so trying to remember first couple of years.
Two years after treatment (lumpectomy, two lymph nodes positive, chemo and radiation) I think I was still having both mammograms and MRIs. every 6 months. I was being followed at Mayo and they typically do not do CTs or ultrasound for screening unless there is something they are concerned about. Around that time, I went from seeing the oncologist twice a year to once a year. A couple times I thought I felt a lump, and they immediately did ultrasound, but it was scar tissue.

For years 3-5, I would have MRIs and mammograms once a year and still do follow up visits with oncologist yearly.

At 5 year mark, my oncologist referred me back to primary with instructions for follow up screenings. Due to dense breast, I alternate every 6 months between mammograms and MRIs.

That is my experience, it will vary for each patient and medical facility.