Transparency under Gimp2.10.6

[dinasset]

On 2.10.6 I did the following:
- open an image (average values of colours)
- add on top a transparent layer
- set mode to darken only
- painted on the transparent layer with a standard black brush : effect=darkened
- changed mode to lighten only : effect=none
Repeated on 2.8.22: got the same results.
Hence, in may case nothing new.