Why does it say I am no longer participating in Family Sharing?

It might also have been fixed if you had simply turned off your device and started it again. It may be the upgrade simply needed to take a look at your settings to be reminded that you were part of Family Sharing. One thing to note with doing things the way you did is to avoid doing it again too soon.

Legal - Apple Media Services - Apple

D. "You can only belong to one Family at a time, and may join any Family no more than twice per year. You can change the Apple ID you associate with a Family no more than once every 90 days. All Family members must share the same Home Country."

September 16, 2021

See Leave Family Sharing - Apple Support. Perhaps you left by mistake, or the family organizer removed you or disbanded the family.

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