Ossian Grr aka "Josh"
It's in the rulebook in the "Game End" section of the Solo rules:
Rulebook p10 wrote:
During the Resolve Adventure Cards step, take note of any “1P” indicators in the bottom right corner of the
Adventure cards. This designation adds an additional requirement the solitaire player needs to meet to gain the
benefit on the card. As in the multiplayer game, if the player does not have the Adventure token associated with
an Adventure card, they are not eligible for the benefit on the card.
Example: The blue “Maelstrom” Obstacle card has the indicator “1P [Max 2],” which
means the solitaire player does not gain the 2 Combat Dice unless they have two or
fewer Armor cards.