A number of possibilities.

When the soil gets cold some plants can no longer easily absorb the nutrients that are present and plentiful in the soil. When it warms up again, they can.

It could be that the rose is getting ready to drop its foliage for the winter.

The plant could use some fertilizer. If winter is coming on, it's usually not the best time to fertilize.

There could be a soil deficiency or an extreme pH that the plant cannot handle.

If you are in the EU likely it's normal winter response. Wait until spring to do anything.

I wouldn't fertilize now. Wait until spring. The rose is going dormant now and you don't want to encourage new growth that will not make it through the winter. Otherwise it looks very happy and healthy so I'd just let it go to sleep for the winter.

hoovb and seil, thank you for the advice.

Caelian

That's a pretty rose. You can get some good compost and put that down in the spring. Some people here like to push straw around the plants after the ground freezes but before the snow piles up around the stems to save more green wood for spring.