How often should I change transmission fluid of my 2020 Prius AWD XLE?

Considering appearance alone, my experience, and I’m “paraphrasing” the miles, but it’s roughly thus:

First (DIY) change at 10k miles: drained fluid is noticeably darker.

Second change at 25k miles: drained fluid is only slightly darker.

Third change at 45k miles: drained fluid is near-indistinguishable from new fluid. Resolve to not do any more changes for a LONG time.

 

From my chats with some seasoned mechanics, changing out transmission fluid too much can be harmful to them. All of them said two things....do it at every 5 or 6 years (50,000 miles) and don't skip. (None suggest doing a break in service, like some do with new engines, I change my oil in new cars at 1,000 miles)
If you've gone over 10-years or 100,000 miles without changing it, or bought a used car that hasn't had it serviced, they said changing it can do more harm than good from what they've seen.
My daughter bought a used 2012 Toyota Sienna van a couple of years ago and didn't have maintenance records. It had 144,000 miles. I checked her transmission fluid and it was dark, but I couldn't smell that burnt smell they can have so I hope and pray the previous owner(s) had done at least one service on it and I went ahead and changed it out. So far, it's been running great so that's a relief.