I am terrible at embedding KSes, but anyway, Realms Beyond is a CRPG sort of inspired by the Gold Box games. At least it mentions them and the box it comes in (if you get physical) looks like one. On the other hand, it also mentions Realms of Arkana, a game which I literally threw out my window after my party died after losing all their shoes while crossing a mountain, causing damage every time they moved.
In Realms Beyond, you will find the tactical turn-based combat of the Gold Box Games, Temple of Elemental Evil and Dark Sun, the world exploration and camp management of Realms of Arkania, the interactivity and living world of Ultima, the choice-driven quests and reactivity of Fallout and Arcanum, and the rich NPC interaction of Baldur’s Gate and Planescape Torment, along with fresh new features that haven’t been seen before in the genre.
Looks mostly like Temple of Elemental Evil (the CRPG) and it will be using the 3.5 SRD, so not too old school, but IMHO, more old school than 5e