Is anyone else getting a 404 error when trying to download "Master of Master Classic (Win/EN)" offline installer from their shelf?

Doesn't work for me either. Neither does the German link.

Since the game has just been updated with a community patch the links are new and probably only lead to the versions without the new patch.

So if you had downloaded and archived the game previously you already have them anyway. And if you didn't the links will most likely be fixed within a day or two if you write to support.

I am not sure what that "classic" is, but if you mean Master of Magic ie, this game:
https://www.gog.com/game/master_of_magic
then yes it downloads just fine for me from the web page. (I don't use Galaxy.)

EDIT: Aaaah! You mean the one in the extras? Yeah it doesn't download for me either.

What is in the Community Update? The Insecticide patch? There's no changelog.

It's the Unofficial Patch 1.50, based on the Insecticide patch.

https://masterofmagic.fandom.com/wiki/Unofficial_Patch_1.50

The one included is the 1.52 version, which is nearly identical to 1.51 but with some additional changes.

Be sure to send a message to GOG Support if you still can't download the classic version.

I was able to download the "classic" version of offline installer. Note that I don't have DLC in my library at the moment.

UPDATE: I was wrong, I have the same 404 error like you guys.
UPDATE 2: It works now. Can someone tell me why French version is so large, are there any additional speech?

No error anymore. Apparently this was just a hiccup due to the new MoM release.

I was wondering yesterday "What the heck is this MoM DLC?!?" but saw the release announcement only today...