[2022] Anno 1800 4K resolution depression on iMac display

Hi. 

From yesterday I have the following problem: Anno 1800 does not support the max resolution of my 4K display on iMac 27" (may 2019).
After the saved game load (or the same with a new game start) the screen shows a hi resolution map as it was according to the settings in the Options menu for a second, but then the resolution of the game is reduced by increasing the scale of the map (the difference in screens 1 & 2).
My attempts to change Options menu Resolution, DitectX and Window Mode settings did not bring any result (screen 3).
The video card model is Radeon Pro 575X, the Display resolution is 5120x2880.
The problem appeared yesterday, before there was not not such a problem from the beginning of the game.

Thank you in advance

PS The game was not updated with the last update.