“The photos in My Photo Stream are already stored on at least one of your devices, so as long as you have the device with your originals, you won’t lose any photos as part of this process,” Apple notes on its support page.

Sounds like a “I do not give apple consent to delete my photos or to charge $4.99 to my account. You have to copy paste it, sharing won’t work.” kind of hoax

That’s why I always have multiple local backups

So this is an old legacy thing in Photos on the Mac? This feels like a non issue