how to get multiple potions?

ive seen people with multiple potions in their inventory and ive always wanted to do that but the game wont let me get more than 30 potions i recently changed to archanist so i realy need healing pls help me

 

I think having multiple potions was removed a while ago. I remember being able to have multiple potions in my inventory, but they wouldn't stack, so most of my hotbar was potions. Now, all of the potion you obtain go straight to your potion stack, as a quality of life thing. I'm pretty sure that now the maximum amount of potions in your inventory is 30.
Just in case it works, try the instant 500 health potions sold in Bremminglar, since I'm pretty sure those don't get added to your stack.