It sounds like you were working on app tracking rather than web tracking, so your timeline makes more sense. The various GA SDKs for different platforms stopped

It sounds like you were working on app tracking rather than web tracking, so your timeline makes more sense. The various GA SDKs for different platforms stopped working a few years ago, forcing a move to firebase-which-is-now-GA. On the website side of things, which is GA's core user-base, Universal Analytics has remained supported up til this announcement.