The Unbroken seal will no longer be available from Destiny 2 Season 19

sportskeeda.com:

The term "Crucible" in Destiny 2 can be a turn-off for a lot of people. Originally marketed as a PvE-heavy looter-shooter, few players tend to prefer beating up AI over Guardians to have a calming experience. However, the PvP side of the game requires some players to participate in quest steps and pinnacles.

While this is better than binding exclusive pinnacles to the PvP, Bungie seems to be completely reworking the seal tied to the Survival playlist activity. In the recently released TWAB (This Week at Bungie), the company sheds some light on the upcoming changes to PvP titles and possible Iron Banner rework next season.

The Unbroken seal is the pinnacle of PvP triumphs next to Flawless from Trials. Survival playlists are bound to require no power advantage, making them somewhat easier for new players while challenging for veterans. Some triumphs even require players to complete objectives throughout multiple seasons.

Bungie's plan with this is to bring it "in line" with other seals in Destiny 2. Players who have already guilded it multiple times will be able to display it. However, the company is planning to bring in another seal for the Crucible Glory playlist, which will have the same challenging factor minus the multiple seasonal objectives.

Bungie said the following regarding their announcement on the Unbroken retirement:

So for any player looking to get the Unbroken seal, now will be the only time to start the grind. Starting Season 19, the triumphs will be removed from the game and will instead be replaced by new ones for Glory ranks.

Bungie also further went on to add:

The word "howling" pretty much seals the deal for an upcoming Iron Banner rework, and quite possibly, new seals.