Where is the changelog in the game page on the shelf? I see it was updated, but I have no idea how. I guess it pulled the latest patch from Wesp5?

It was updated to the latest unofficial 9.6 basic patch, you can see it in the file name:
"1.2 UP 9.6 Basic (GOG-8)"

OK, but why is changelog missing?

No idea. Here is the one from my patch, only the basic patch changes:

Blocked way into locked SM junkyard and corrected Chunk levitating.
Made Sin Bin ATM machine not vanish and Romero sit after boinking.
Fixed Givanni sound schemes and monitors in Skyeline and SM clinic.
Delayed Mercurio cutscene to make player move where he can see it.
Improved weapons, timings, ocean and widescreen cut of Ming ending.
Made crackhouse girl flee and hid two mirrored theatre door signs.
Removed restored weapons from basic and restored all the stats too.
Recompiled Kamikaze Zen map to fix vent without exit and lighting.
Corrected bad elevator light at Red Dragon and Jezebel's door lock.
Fixed decapitation shot and restored basic drugbox value and rain.
Unified keypad sounds and fixed wrong detection and sounds on Dane.
Fixed museum door not being locked and some minor dialogue issues.
Lowered Asylum music volume after loading and fixed minor map bugs.
Added original Japanese and Russian words to translated subtitles.
Fixed Empire mafia reaction and reduced pier artefacts and effects.
Updated SDK and fixed audio loop at Fu Syndicate, thanks Psycho-A.
Made manholes in Venture Tower cellar and Ocean House sewers close.
Fixed bad Kerri dialogue start and delayed Jeanette and Ming ones.
Used autoexec.cfg to fix talk dsp sound and frame rate door issues.
Enhanced some areaportals at Leopold Society and Giovanni Mansion.
Recompiled Zhao's Warehouse to fix huge doors vanish at a distance.
Fixed Nosferatu causing Masquerade violations exiting Luckee Star.
Adjusted volume of some NPC lines and corrected NPC coughing loops.
Fixed some Ocean House rails, areaportals, shadows and a map hole.
Made persuaded Chunk not attack and incapacitated drop gallery key.

Thanks! I hope GOG will fix it and will include changelog in the game page.