What are your working times in a hover. I have between 26 to 27 minutes. From take-off to self-landing at approx. 4%. One of the batteries is clearly weaker. I have about 25 charging cycles.Shouldn't there be more?

Personally, I would not let the battery get down to 4%. The displayed capacity is only an indication, and you might find the aircraft decides to land somewhere that is not safe to land.

I have a request. Let's stick closely to the answer to my question. The drone is not flying, it hovers in the air in the room. What are your working times?

No .. that's about right.
If you want the drone to be inthe air for longer, you need to fly rather than hover.
DJI list the conditions required for max time in the air in the specs:
Max flight time:  31 mins (measured while flying at 4.7 m/s in windless conditions)

The user manual from November 2020 says that the maximum hovering time of the drone is 33 minutes and the flight time is 31 minutes. This makes logical sense because there is air resistance on the fly. The flight test is difficult to perform under reproducible conditions. The test is already hovering like this, especially indoors. The problem is that the result is below expectations.