You can sort the topics by the number of views. Naturally, older topics got more views than newer.
There are no votes here, and in general the issue tracker is more relevant when it comes to specific bugs/feature requests. There is an option to "star’ an issue but I would not rely on it as a popularity metric.
All major releases and their dates are available at Releases · bardsoftware/ganttproject · GitHub
You can do some simple maths to calculate the frequency. Minor maintenance updates are partially listed in JSON file: https://storage.googleapis.com/dl.ganttproject.biz/updates/ganttproject-3.2.3200.json
I remove some updates if there is a subsequent update which includes them (e.g. 3241-3245 are missing because they are included into 3246)
We have no feature usage telemetry. GanttProject follows the EU privacy laws, so if you see no consent about sharing such data, it means that we do not share it.
Typical sectors, judging on GP Cloud paying customers and on project files which people share here and privately, are construction, engineering, media production, IT administration, medicine, and other projects where tasks are measured in days and naturally have dependencies 
