Some ideas I might pursue at some point.
When air humidity reaches a threshold value, get an alert on my phone.
Make sure to be alerted only once.
Based on the current weather (temperature and relative humidity outside) I want to know what humidity I can reach at room temperature.
Have a particle sensor indoors to follow its data. Maybe have an alert.
For the nearby river, collect gauge data. Have a warning when it reaches a threshold level.
I have https://github.com/marians/lanuv-nrw-water-level-api to make data from the official source more accessible. Next I would need a way to have the latest value for the relevant river in Home Assistant.
Use Grafana for more powerful data visualization.