You can't access your full mental faculties, and you have trouble casting spells.
Kind
Condition, carries a value
Value
1 or higher
Group
Lowered Abilities
Your thoughts and instincts are clouded. Stupefied always includes a value. You take a status penalty equal to this value on Intelligence-, Wisdom-, and Charisma-based checks and DCs, including Will saving throws, spell attack modifiers, spell DCs, and skill checks that use these attribute modifiers. Any time you attempt to Cast a Spell while stupefied, the spell is disrupted unless you succeed at a flat check with a DC equal to 5 + your stupefied value.
Lowered Abilities conditions
Player Core groups Stupefied with Clumsy, Drained, Enfeebled.
Source: Pathfinder Player Core, p. 446
Bring Stupefied into a Pathfinder 2e game with The DM Screen.