I would also find this useful
I'd look at logging it yourself.
As I use relay switching, I can only grab the heating percentage from the Tado API. You may have a different measurement in there if you use digital bus (I don't know). Mine shows 29% at the minute.
I monitor the flow and return temps using a pair of DS18B20 sensors connected to Sonoff TH16s which I send over MQTT. I grab those using Node Red and shove them in an InfluxDB. I visualise that in Grafana like anyone would.
I could gather the demand (percentage in my case) from the Tado API and overlay it. If you have an actual requested flow temp in your Tado API, rather than a percentage, you could use/overlay that.
I already requested this please add support here
I've added the Tado demand percentage on the right Y-axis.
It's just a number of free tools that I just connect up.
For the API, I use Node-Red and it can connect to the Tado API and grab data. That runs on a Raspberry Pi.