For a while now, I've only been able to download Darkest Dungeon 2 and The Binding Blade DLC through Galaxy, but not the newer three. I usually have this problem when purchasing new DLC as well. Is there an option or setting I'm missing? Do I need a fresh install?

On a side note, I haven't been able to download the last few updates for Project Warlock 2 either.

You say that you cannot download these updates. What happens if you try to download them?

I think I should have mentioned that this is for offline installers.

If I go to the Extras tab to get the offline installers, I'll click on one and the download does not start. In Project Warlock 2's case, I get a "download failed" message and a red bar in my download progress tab.

Sometimes the database does not get refreshed which can lead to the issue you are describing.
You can try this:

https://www-diashow-com.translate.goog/gog/anleitung.html?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp
(It's auto translated and was originally German - if you have questions just ask me)

If you only use Galaxy for GOG games you might as well just let Galaxy rebuild the database completely. All you need to do is to rename the storage folder in "\ProgramData\GOG.com\Galaxy". Galaxy will rebuild the database from scratch when you restart it. Afterwards you just need to rescan your installed games (which should be pretty fast and easy simply by scanning the folder of your install directory).

Great, thank you!