As my challenge was solved before I even finished my afternoon swim in a lake (hot day again here), maybe I shall give that trial announcement in hranhuk's post comment - a more official status.
For a wider reach, and better visibility.
Here is a crop of my comment:
Get your smart brain a kick, and pick those 200 POB. :)
First hint (if you ask) - after 24h from this moment, 17:40 UTC, 19.07.2021
Hint #1 - It's in Northern Hemisphere
Hints #2, #3 & #4 is here: