Drops the label tracking pin kept through the 3.x upgrades, so Argo CD uses its default argocd.argoproj.io/tracking-id annotation. Labels can be copied by other tools (cert-manager's ingress-shim copied app.kubernetes.io/instance onto Certificates); the annotation names the exact resource. Every app gets synced once right after, so resources removed later are still recognised for pruning.
Argo CD 3.0 switches the default to annotation tracking. Per the 2.14->3.0
upgrade notes, a resource whose first sync after the switch is a deletion
gets orphaned instead of pruned. Pinning label tracking (the 2.14 default,
so no change today) keeps the upgrade to 3.x free of that; moving to
annotations can follow once everything runs 3.4.
Ruben Hensen