Even if you expand the search criteria to include video games, there just aren't many deeply strategic discrete-time games that weren't invented centuries ago and have players online at any given time. Here I exclude games that are perpetually changing and/or have strategies locked behind progression systems and paywalls, such as TCGs and virtual deck builders. The very few exceptions I found were niche Discord communities around games like Tak, Hex, or Advanced Wars.
When did we as a society lose the appreciation for these things? I get why including a component of dexterity in strategic video games (e.g. RTS) is to take full advantage of the medium, but all this in conjunction means we are very likely never to see another deeply studied cerebral game like go, chess, shogi, mahjong, etc. arise ever again.