Here are some classics from that period that are on sale on GOG.com and have open-source engine offerings:
The Curse of Monkey Island (classic funny point-and-click adventure, ScummVM)
Theme Hospital (tongue-in-cheek management sim, http://corsixth.com/)
Arx Fatalis (would have been Ultima Underworld 3 if they could get the rights, Arx Libertatis)
You can extract the data files using either the newest version of https://constexpr.org/innoextract/ or using Wine.