Identifying That 90s PC Game: Castle, Alchemist, Blacksmith, FMV Actors

You're likely thinking of The Journeyman Project: Pegasus Prime (1997, Mac/PC; 1998 PS1). The "knight or servant" choice is probably a misremembered disguise mechanic.

Why Pegasus Prime Fits

• Castle setting: Temporal Security Annex has a castle-like aesthetic.
• Characters: Blacksmith, alchemist, king, jester appear.
• Live-action FMV: Real actors green-screened into 3D environments.
• Role-playing: You play Agent 5, Gage Blackwood, who disguises as various roles—not a knight/servant choice at start.

Other Candidates

• Dragon Lore (1994) / Dragon Lore II (1997): Fantasy castle, alchemy, blacksmith, FMV actors. Play as Werner, a knight-in-training.
• Blade Runner (1997): Heavy FMV, choice-driven, but not a castle setting.

Most likely match: The Journeyman Project: Pegasus Prime (often misremembered due to disguise missions). GOG sells a Windows-ready version.