NOTE : This game updates regularly, so there might new methods of gaining xp for the hunt pass in the future.
Credits to Leo Ascendent: "For those curious, with the update, you basically get freeroam with up to 6 people who can drop in at any moment. You get Hunt Pass XP, varying on difficulty and number of times the monster has been killed (I was earning about 11xp but it went down to 9xp after repeated kills). Do this, plus the bounties, and you should be able to easily level up 5 times in a few hours."
Not a direct solution but serves more of an information guide: There are 50 levels total, and you can get hunt pass levels by
i. completing weekly challenges (Diffuclty: Varies and it is doable)
ii. collecting a certain item (season 5: the item is called deathmarks the item changes every season and its just like picking something up for a daily objective) within ramsgate (Diffuclty; Easy)
iii. breaking behemoth parts on hunts (Difficulty: Easy but its RNG and grindy)
iv. pay real money to max rank the hunt pass. (don't recommend if you are gonna go for all the achievements but hey its your money) (Diffuclty: Varies, some people are rich and some don't feel the need to spend extra in-game)
Hunt pass information: To the unknown this might be like a pay to win service. It can be considered in a way because owners of the elite hunt pass have more consumables and gain more items when they level up their hunt passes, but not to be considered a crazy advantage towards players who do have the normal hunt pass. Most of the weapon/clothes are purely cosmetic and don't provide any additional bonus.
Note this information guide might change in the future because the game is being constantly updated and I played this game on PC, maxed out hunt pass season 4 (previous seasons: 3,2,1 does not seem to meet the requirement according to DarkSynopsis). As soon as I signed in the xbox version, I got the achievement even though the xbox version started on season 5.
Edit : Credits to MushaConvoy for estimate completion
-Its only 5 points per daily Deathmark, so collecting all 10 is half a level. If you only account for weekly challenges + daily Deathmarks, you should earn 9.5 levels each week. 5 weeks and your Hunt Pass will be at maximum (35 days), assuming you pick up some extra points while fighting behemoths for the weekly challenges.