Wolfenstein: The New Order had a blue dot in my library, indicating an update since I last downloaded the installation files, and indeed the current installation files have different sizes than the ones I originally downloaded, but the version number has remained the same ("1.0.0.2 hotfix"), and there's no changelog.
So, what has changed?

Looks like there was rollbacked update. Or not rollbacked? In both way likely that new installers have 2024 date/digital sign date even been old file name and even if there is actually old build (rollback).
Probably very exact old setup restored. That mean no need to redownload.

What changes? Who knows. There was such silent updates for more Bethesda titles at differ times. There is more on GOG in general. There is more rollbacks. Sometimes real upgrades got reverted to downgraded version. Star Wars Battlefront 2 or Legacy of Kain Soul Reaver.
Although SWBF2 was only GOG-Galaxy update and got removed even from Galaxy. Soul Reaver was GOG-Galady+GOG builds update and both got removed (cannot be chosed in Galaxy).

This subj uodate happened only for offline installers. At least we know no and supposed to be no updates for Galaxy. Thats why i assume rollback. There was no rollback though for Fallout's titles got silent updates. So hotfix of hotfix possible as well.

Look to http://www.gogdb.org/ for reference.
This website track GOG-Galaxy builds and list them. Next if they removed entirely or hide to public they remains on website. Same for very old builds from 2015 not all available today, still listed on gogdb org. That mean we know there is no reverted updated in Galaxy. On public. For info about private branch - those builds which counted as published too while more in-dev possible - look to Galaxy Builds API link there on website (there is only counter of published builds and info about current available to public without hidden/removed ones, so if only 2 of 2 visible mean any else removed entirely including from private branch, nothing more to know)

Thanks for your detailed reply, and thanks for introducing me to GOG DB (I use SteamDB regularly, but wasn't aware GOG has one as well) :) too bad it's just for Galaxy, as I don't use that, but it can still be useful.

I suppose the only way to know if there's an actual change in the game in this case, or wheter it's just a change in the installation files, is by installing both the old and the new, and compare the contents, but that's too much of a hassle lol