Story related and cannot be missed.
*** Spoiler - click to reveal ***Far Cry 6 has a total of 56 operations, or main missions if you will. They are spread over 5 different regions of the open world map. Complete all of the 56 operations, beating the game, and the achievement will be yours. Not too difficult to be honest, even in Action mode.
- Isla Santuario (starter island/main story)
- Madrugada (Monteros storyline)
- El Este (The Legends storyline)
- Valle de Oro (Maximas Matanzas storyline)
- Esperanza & Isla Del Leon (end game/main story)
Each of the 3 main map regions has their own story line, tying into the games main story. You can go just about everywhere as soon as you leave the starter island, save the end game area that is locked into the story. It is recommended (by the game at least) that you take on these respective regions as you progress through the game as they increase in difficulty as seen on the game map. The story progression also makes more sense doing them in order, but the decission is utimately yours. I did however travel back and forth across the map completing quests and objectives as I saw fit. Once you enmass loads of resources and build an arsenal of powerful weapons, almost nothing will stand in your way.
Plowing straight through the story is most certainly possible, but you will want to explore this tropical paradise island collecting gear, resources, weapons, gadgets, collectibles, amigos, allies, vehicles etc. The stronger you get, the easier the end will be. Oh, and get the wingsuit asap by building the Hideout Network in your first Guerilla Camp. It will help immensley traveling around the vast island of Yara as smoothly as possible.
After completing the game you are put back in Yara with all your stuff that you have aquired (weapons, vehicles, amigos, gear etc) and can continue to get achievements. All the collectible achievements will probably be easier after the end game as you will have unlocked more fast tavel points during your time in Yara.
Beating the main story will not lock you out from getting all the achievements in the game, as none are missable. It does however increase the strenght of the enemies in the game, but at this point they will be no match for you to handle.