Hmmmm, if the mc has the required materials, he can make most potions and by that, he can make a potion that mutates his genes to make him powerful or to mutate a plant's genes to grow something new or grow iron if not iron dust, then probably a potion that turns iron dust into iron.
A potion that also somehow gives experience or change his stats or give skills seems impossible. However, he can make the potions like in minecraft that you throw that explodes powerful enough to kill.
But then he needs materials and materials can be obtain through cultivating which needs materials. So trading with merchants with potions through a medium to get money or items is the only way. And if he does get a skill that gives him infinite storage or a small pouch that gives him a big storage. Then he can stock up deadly potions or potions that give power-ups and go farm up levels.
If I were him, I first get money, then materials, then stock-up harming potions that is silent, blindness potions, potions that give you invisible, potions that give you high jump and fast speed and potions that heighten my senses.
Then, i run around so fast while throwing potions to monsters in a dungeon or forest and get levels.
Ill do that until I get so powerful then prolly make a harem.
It takes time but its the usual same thing for me, a gamer, grinding.
And let's say I meet an opponent that is immune to abnormal status, then I just get powerful and learn some skills and kill him
Edit: I also make a potion that makes me an immortal and a potion that kills me.
Edit: and also some aphrodisiac for researching purposes.