we’ve been using Triton detectors at my school for a while now, they catch both nicotine and THC vapor fast and it sends an alert right when someone vapes, even picks up small amounts. it’s probably the closest thing you’ll find for what you need.

If everything was working on 2.3.1, you should be able to pick up right where you left off. Most sensors built with 2.3.2 will still communicate fine with a 2.3.1 gateway, so you don’t need to overhaul anything unless you want to.
Home Assistant still supports MySensors, so you can integrate the gateway either over serial or via TCP if you ever move it off the Vera. Sounds like a fun project to revive!