I checked the running of manjaro-kde-21.2.0-211220-linux515.iso linked in the Manjaro 21.2.0 Qonos released! the issue mentioned in the first post is solved: storage section summary now is not doubles.
I saw stable branch updates release and a bit postponed release of stable ISO. So the idea discussed in that thread was implemented. May be the approach will be changed/optimized in future. But I happy that the idea got a spin to try it out. Thank you!
I see no reason to leave the topic open: the issue was fixed, the idea was implemented. Mods, please close the thread.