What flow temperatures are you currently running?

The problem is that it is a standard general contractor/prefabricated house provider design

The whole thing is designed for a maximum of 30°C flow temperature

So what now? 30FT is a dream! Why don't you open everything up as much as possible and turn down the heating curve?

Unfortunately, the appropriate taco setters are not always installed.

These adapters are good for adjusting the flow volume. Does anyone know where to buy these adapters?

That’s why many Taccosetter valves also look like they have zero flow. According to calculations, at 20°C I hardly have any adjustable flow, and in reality, since I only want 18-19°C, even less.

You have (still) not understood the underfloor heating system.
Finally give the "box" volume flow.

So I have now given the list volume flow:

Kitchen 1 65 m. 1.0 L/min
Kitchen 2. 54 m. 1.1 L/min
Living/Dining 1. 117 m. 0.8-0.9 L/min
Living/Dining 2. 91 m. 1.0 L/min
Living/Dining 3. 97 m 0.9 L/min
Sleeping 1. 101 m. 0.9 L/min
Sleeping 2. 98 m. 0.9 L/min
Bathroom. 73 m. 1.0 L/min
Guest 1. 77 m. 1.0 L/min
Guest 2. 71 m. 1.0 L/min
Hall 1. 37 m. 1.1 L/min
Hall 2. 35 m. 1.1 L/min
WC. 39 m. 1.0 L/min
Utility room. 49 m. 1.0 L/min

According to heat pump display now ~768 L/h
Heating curve 0.1
Desired temperature 20°C

Now it just has to get colder again.

According to the heat pump display now ~768 L/h Heating curve 0.1 Desired temperature 20°C

There you go, it works. You can reduce sleeping to 0.5 each and add the 1 liter in the bathroom. Have you checked the heating curve in your documents? What is "delivered" at 0.1 / 20 at AT 0? That is certainly too little. How are the RTs currently?