What happened to Domoticz ?
Dietpi 9.8.0 Bookworm .
Installed it with 
sudo bash -c “$(curl -sSfL https://install.domoticz.com)”
and it works fine Rpi 5 .
why doesn’t it show on the software list anymore?
At the beginning of the year, we released the software title for x86 only. This had something to do with libssl3. See DietPi-Software | Domoticz: Enable for x86_64 Bookworm/Trixie systems by MichaIng · Pull Request #6882 · MichaIng/DietPi · GitHub
Whether this has changed in the meantime would have to be checked again.