As the titel suggest, I am trying to install the path 1.06+. However this is not working properly. The exe starts and attempts to do so, but has several hundred (?) "Error modifying" notifications in the patch log.

Same here.

The offline installers have 6 different variants of patch 1.0.6. It's somewhat messed up.
The best bet is to install GOG Galaxy and let it verify the file integrity and auto-update.
And the latest patch is 1.0.7

Currently I am running 1.0.6_(24207)

the offline installers available to me:
1) patch_pathfinder_kingmaker_1.0.6_(24207)_to_1.0.6_(24253)
2) patch_pathfinder_kingmaker_1.0.6_(24253)_to_1.0.6_(24283)
3) patch_pathfinder_kingmaker_1.0.6_(24283)_to_1.0.7_(24296)

The first one should work, but doesn't. So it is not a matter of me not running the correct file ;-)

Sidenote: I am nor interested in using Galaxy, for various unrelated reasons.

When I read "Error modifying" my spider sense were tingling. Did you try running the exe as administrator? 'cause it sounds that you are not granted permission to, well, modify what you wanna modify.

Yes I am. That was the first thing I checked :-D

May we see those? Or do they actually just say "Error modifying"?

Worth a try tho you might have done that already: will it let you skip the 24207 to 24253 patch or do you get a "wrong version" error in that case?

Hast du die Datei direkt herruntergeladen oder über den GOG Downloader?
Prüfe deine Datei "patch_pathfinder_kingmaker_1.0.6_(24207)_to_1.0.6_(24253).exe" bitte mal:

Dateigröße : 928.489.112 Bytes
MD5-Prüfsumme : 14b1d6865cc1841e2f6c88ef067254a4

Maybe your current game installation got corrupted in some way and the offline patch cannot determine what is corrupted (In some not so rare cases it happens).
Relying on offline patch installers there is no way to check the files integrity of the previous installation.
I would suggest you download the latest complete game installer and reinstall the game - skipping the patching process altogether.
From my own experience - I had so much trouble applying offline patches for other games - especially for games with that amount of consecutive small hotfixes - that I decided to GOG Galaxy to save myself the trouble and time.

If nothing works for you then please contact the support, send them the log files and maybe they will be able to help you.