I just had a session and there was an argument about this. In the DMG page 187-188 it shows potions of healing in the magic item section. In the PHB page 153 it says they are magical. On DNDBeyond it is considered both magical and mundane when you go to add equipment to your character. One player was saying they are always magic items and another was saying that according to dndbeyond it isn't always a magic item. Which person is correct?
Potions are magic items.
From the Dungeon Master’s Guide:
Potions are consumable magic items. Drinking a potion or administering a potion to another character requires an action. Applying an oil might take longer, as specified in its description. Once used, a potion takes effect immediately, and it is used up.
Potion of healing (all rarities) is found in the magic items chapter of the Dungeon Master’s Guide, and potions are explicitly described as magic items.
We also find a common potion of healing described in the equipment section of the Player's Handbook:
A character who drinks the magical red fluid in this vial regains 2d4 + 2 hit points. Drinking or administering a potion takes an action.
A potion of healing is a magical red fluid.
Additionally, in Eberron: Rising from the Last War, there is a section called “Creating Common Magic Items”, which says:
But if you have a dragonshard, you can more easily create a common magic item.
To create such an item with a dragonshard, a character must have proficiency in the tools used to create a nonmagical version of the item or proficiency in the Arcana skill. For example, a potion of healing can be created by a character who has proficiency with the herbalism kit.
In this section, potion of healing appears in a table column labeled “common magic item”.
Does the phrase "a character must have proficiency in the tools used to create a nonmagical version of the item" imply that you can create mundane potions of healing with an herbalism kit?
No. Rules for creating potions of healing with an herbalism kit of found in Xanathar's Guide to Everything, here we see:
Potions of healing fall into a special category for item crafting, separate from other magic items. A character who has proficiency with the herbalism kit can create these potions. The times and costs for doing so are summarized on the Potion of Healing Creation table.
Even when created with an herbalism kit, they still count as magical items.
The DDB character sheet is not official rules material.
Every once in a while DDB’s implementation of the rules into the character sheet tool leads to confusion as some things are misrepresented. Here is an example. The rules are quite clear that potions of healing, even common ones, are magical, and anything in the character sheet implying otherwise is an artifact of the character sheet.