I've been update unity 2017.4 to 2019.4 and build my game to ios.
Problem is change Social.localuser.id type, start with "G:xxxxx" to "T:xxxxxx".
I search some research, and find Apple change player Id gameCenter id to TeamPlayerId,PlayerId.
My Game is live and to migrate Apples new id type it's need least 3 month use gamecenter id type.

-- 1. how can i get legacy gamecenterid?

and Unity 2020.1.6 release note in api section. "iOS: Added: Added a public accessor for the legacy Game Center player ID, to give games an easier pathway to migrate to the new ID types in iOS 12.4".

-- 2. But i don't know how can get legacy Game Center player ID?

-- 3. And Any plan to update, unity 2019 lts version to get legacy type Game Center Player Id?

thank you for reading.