I would assume Steam Deck 2 isn't dropping before at least H2 2026, if not later, if they didn't bring it out with the announcement of the other devices.
Valve's only official statement as far as I know is that it will come when they see a significant enough hardware upgrade to warrant a new system. If they don't move to ARM, AMD's Medusa APUs are their next architecture with major upgrades, so I would guess that Valve would order another custom AMD chip but based on Medusa, which won't release until at least 2027. I would guess at least H2 2027 but probably early 2028 for an AMD-based Steam Deck 2.
Valve's only official statement as far as I know is that it will come when they see a significant enough hardware upgrade to warrant a new system. If they don't move to ARM, AMD's Medusa APUs are their next architecture with major upgrades, so I would guess that Valve would order another custom AMD chip but based on Medusa, which won't release until at least 2027. I would guess at least H2 2027 but probably early 2028 for an AMD-based Steam Deck 2.