Having played Divinity: Original Sin and the Shadowrun series, I'm left with a turn-based RPG itch. Any recommendations (other than D:OS 2)?

Arcanum. Best character creation system ever.

Age of decadence is pretty good imo, I really liked its turn-based combat. There's a demo available, so try that and see, if you like it.

Fallout 1 and 2 are my favorite in the genre. Underrail appears to be held in very high regard as well.

If you want to check out something with very good turn based combat that's lighter on the rpg side, then Jagged Alliance 2 is an excellent choice, and for great turn based combat with even less rpg elements then Xenonauts or OpenXcom are great choices

Hell yeah, Arcanum is amazing!

Check out ATOM RPG, it's not bad at all. it's more like a fallout 1&2 then anything else.

I have yet to try it myself, but Wasteland 2 was recommended to me by a friend. Currently it's on sale for %50, and includes the first Wasteland.

Trails in the Sky parts 1, 2 and 3.

and

Trails of Cold Steel parts 1 and 2.

Mary Skelter.

Play Gorky 17

The Bard's Tale Remastered 1-3, Battle Brothers (As much RPG as it's tactical and strategic but you should play it), Geneforge, Avernum, Expedition Conquistador and Vikings, Temple of Elemental Evil, Most of the Forgotten Realms Collections like Eyes of the Beholder, Pool of Radiance and Dark Sun.

I second these.

If you are looking for something similar to Final Fantasy Tactics, Fell Seal scratches that itch. And the level of difficulty is very customizable, so you can have it as hard or as easy as you want.

The other recommendations above (Fallout and Fallout 2 especially) are also gold.

Grandia 2 has a unique combat system, although it's obviously a console-style game. Speaking of console-style games, I like the Hyperdimension Neptunia series as well. Otherwise, all my bases are covered above, even Fell Seal, which isn't really like the others (it's more strategy than RPG).

Eye of the Beholder is not turn-based; otherwise great suggestions. Another two would be Albion and Anachronox, and then maybe the Realms of Arkania trilogy, provided the OP is fine with such old 90's games.

As for newer games, I think Pillars of Eternity 2 now includes a turn-based mode as well, doesn't it? Not full RPGs but offering tactical turn-based combat: Blackguards, Legends of Eisenwald,

Isn't Grandia 2 a real-time, rather than a turn-based RPG ?.

I haven't played it myself, and am just going by what I have read.