QFNS I suppose there is no way of gaining free cards in MTG after the initial unlocks ? I'm not opposed to paying for boosters, as its the origin of the game, but it's true that I would vastly prefer some free stuff too.
No, I'm not stating the obvious, I mean the feeling of progression, of unlocking stuff
Oh there absolutely is a way to gain cards without paying money.
Here's how the economy of the game works:
When first starting out you get several tutorial missions which unlock preset decks of the various colors, and then several multi-color decks. These decks and the cards in them are completely free. You keep them forever (or until the servers shut down, I guess).
After finishing all of those you get into the standard economy of the game. You earn gold by doing quests, weekly wins and daily wins. You will also earn XP toward the mastery pass (like Apex or Fortnite) which at each level will reward you with either nothing, a cosmetic, or a card pack. The mastery pass also has a paid tier which has more rewards on it (more cosmetics, packs of different sets, etc).
Beyond this you can spend gold on packs (1000 gold = 1 pack of 8 cards (5 common, 2 uncommon, 1 rare or mythic rare), drafts (rewards vary based on wins), or other events . Typically it is good advice to do drafts to gain cards of a new set as it is a better value for the gold per card (you keep the drafted cards in most draft formats). The best value for gold entry is Quick Draft which is a draft against bot opponents and then you play the games against other humans. There are also draft formats where you draft with other actual humans, but the upfront costs are higher. I have never had an issue getting into a draft.
However it does take some upfront investment of gold or gems (the money currency) to get into a draft and you really only make back your investment if you get good results. So while "rare drafting" is a thing people do (drafting every rare card they see in order to complete sets), you end up with better rewards if you just draft good cards and make a better decks.
The other currency (gems) can also be used for basically the same purpose as gold but obviously is less overall investment as it is directly $. It is possible to convert gold into gems via some events (like drafts) where you enter with gold and the rewards are in gems. Its good to keep a look out for these as they are the only way to convert from gold to gems directly.
Beyond that, the game really only rewards you for playing every day, finishing your quests and your daily or weekly wins. If you keep up and do all those things (or most of them, it is not necessary to do ALL of the daily wins every day) you can eek out a decent free to play life. However when new sets release expect to get stomped by new cards for a while until you can afford to make the next powerful deck.
Speaking for making decks. This game uses a wild card system for crafting. You earn wild cards of varying rarities and use those to craft cards that you don't have or haven't opened in a pack. This gets a bit annoying when you need to craft a rare card for instance, and you don't have any rare wild cards. You are stuck. Even if you have Mythic wild cards you cannot "trade down" and you cannot trade up from uncommons or commons either. I personally have over 100 Common Wildcards and maybe 80-90 uncommon ones (and this is after going on a crafting spree from the last set. The rare WCs are going to be the hardest to get eventually. Mythics are less useful overall than rares because there are typically land cards at rare and not usually at mythic.
You will almost certainly want to be crafting some rare lands after you figure out what kind of decks you like and what colors you want to be in. It isn't sexy but better mana is almost always the right choice for a stronger deck.
Let me know if you have more questions, I'm happy to chat.