Underfloor heating air-water heat pump. House too warm when the sun shines

I think there are different theories about that. I'm now testing (though modulating) with 1 degree less setpoint at night and 1 degree more during the day.
You probably won't really notice the night setback on the room temperatures, that consideration is correct. However, your screed still cools down. So the "problem" you have the next morning is that when you turn it back on, more energy is needed to reheat the screed. The question is what is more effective, and I've often read that reheating can sometimes require more energy than you save by turning it off at night.
Maybe you could try it "stepwise." So just throttled? Does your pump have a night mode or something similar? But testing only really makes sense if you haven't adjusted other settings at the same time.

I do heat with gas, but I also tested turning it off at night and then reheating the screed. => Running the heating continuously is ultimately cheaper than turning it off for 6 hours at night and then reheating.... and of course much more comfortable.

I do heat with gas, but I also tested turning it off at night and then reheating the screed. => Running the heating continuously is ultimately cheaper than turning it off for 6 hours at night and then reheating.... and of course significantly more comfortable.

I would have thought more about lowering the return set temperature by 0.5-1 degrees so that the heat pump has to heat/run for a shorter time.

With gas, it's so clear, where should any advantage come from?
With air-water heat pumps, it's different.
They benefit both from higher outside temperatures and, if available, from using their own photovoltaic electricity.