You can currently run certain cards that should not be legal in the Alchemy format in Alchemy. This was tested on PC.
Steps to reproduce:
1. Create a deck for the Timeless format. Include only Alchemy legal cards. Then, add cards that an Alchemy card conjures into the deck as well. Examples are Siege Rhino (conjured by Call the Crash) or Lightning Bolt (conjured by Idris, the Hydrostatic Surge).
2. Switch the deck's format to Alchemy and return to the deck view screen. The illegal cards will be highlighted in red, but no prompt will appear to inform of illegal cards for the format.
3. Exit the deck view screen. Again, the deck will appear valid.
4. Enter the Alchemy queue with the deck.

Expected results: The deck should be considered illegal, as it is when using other illegal cards that aren't valid in the Alchemy format.
Actual results: You can queue into the game with the deck even though it contains cards that aren't valid for the Alchemy format.

Attached is the image with an example of a deck containing the illegal conjured card that is allowed to play in Alchemy.