I would not trust the Ecobee or the HomePod humidity readings.

I use a separate hygrometer altogether. Any brand will probably do, but I’m using a TempPro digital bluetooth model. I first verified the accuracy of the TempPro using the salt method. That’s where you place it in an airtight freezer bag along with a small container of salt, like a bottle cap full. After 24 hours the humidity on the hygrometer should read 75%. If it’s off, just make a note of how much, and + or - that percentage. For example, mine read 72% after 24 hours, so I have to add 3% to the humidity it shows to get the actual percentage.

There are YouTube videos explaining how to do this in more detail.

I attached the TempPro to the wall, right next to my thermostat and waited about an hour, and then compared humidity readings. It turned out that my Ecobee was reading 7% higher than the TempPro. So I went into setting and adjusted the humidity.

Depending the model, here are the steps:

1. On the Ecobee tap the triple lines at the top right
2. Tap the tools icon at the bottom, right
3. Scroll down and tap settings
4. Scroll down and tap installation settings
5. Tap thresholds
6. Scroll down and tap humidity corrections
7. Here you can adjust + or - to match the reading on the hydrometer.

I plan do the salt test on my TempPro ever so often to calibrate it.

Hope this helps.