How to descale a floor-level shower drain?

I have a walk-in shower with an integrated shower drain. I clean it regularly. After about two years, slight limescale deposits have now become visible. Of course, I can descale the removable part very well, but unfortunately not the drain itself. How should I proceed here?

Seal the drain and then pour in a mild mixture of citric acid? The shower drain should easily withstand that since it is made of stainless steel, right?

Actually, it is sufficient to spray with a descaling solution, let it work, and then brush. But the suggested way also works. The stainless steel doesn't mind.

If you remove the cover, you can easily clean the channel. It will then be exposed! I don’t understand!‘...

Cleaning is not the problem, but removing the limescale deposits.

Since I generally do not use ready-made descalers and my home remedies (citric acid and vinegar) are too liquid to stick, I have to soak the limescaled areas accordingly for about an hour.

Since I generally don't use ready-made descalers and my home remedies (citric acid and vinegar) are too liquid to stick

Thicken with flour or starch? ;)

Yes, I could also try that.