You aren't meant to get them, Bungie never got around to moving them (amongst a bunch of other triumphs) to the Legacy section and ultimately with the last few updates prior to End of Service happening they weren't risking updates that could break things. In the past Bungie have had issues with moving triumphs, including one major issue being a full rollback happening in 2023 due to them moving triumphs from active to legacy. Good chance they saw the risk attempting to move triumphs posed and decided against it.