Anyone know if it's possible to somehow download mods from Steam workshop directly via browser (so they can be used in the GOG versions)?

I have never heard of a way but did you try talking very nicely with the creator about a version not tied to Steam? In many cases that is a lost cause though.

It's not so much about that, most mods are available outside steam (on moddb or wherever), the problem is that they are sometimes several versions out of date.

This might help?
https://www.gog.com/forum/shadowrun_series/how_to_get_steam_workshop_mods_without_using_steam

Bookmarked, now that was something useful to know.

Not all workshop games can be downloaded. See this, more extensive and organized thread for details.

there used to be an extension for greasemonkey, but iirc its broken now (since the way, it used to trick steam, now patched).

Personally, if game, Im looking for, has mods - I tend to buy base version on sale on steam, then wait for gog connect. Or, well, buy it twice (once for workshop and once on gog). Thats why I hate workshop tho :/

Steam workshop doesn't always work for games on GOG. For gal civ III in an example, custom civs and ships work but with Stellaris, I can't get them to work (need to be in the mods folder in documents) and have MP with Steam. Kerbal Space Program workshop mods work... if you place the craft files directly in the crafts folder and do the same for missions. I think Tropico 5 works with workshop mods and nothing has to be done but check that. I am unsure about Project Highrise either in that regard.

I use the Enhanced Steam Workshop Downloader from greasyfork.org with Tampermonkey (since Greasemonkey no longer works in FF). Anything can be downloaded, as long as the game publisher allows it. See the thread I mentioned above for a list of ones that do. There is no "patched hole" -- it's just that publishers don't put in the minimal effort required to allow non-Steam downloads. All workshop downloaders I know of use the same technique, which is blocked by the same inconsiderate publishers.

Not long downloaded Dungeons of Dredmor again... but all the mods i wanted were on the workshop. And the mods only downloaded while using steam's version of DoD. Though afterwards easy enough to move to the HB version...

A side note, can't optimize DoD's png's.... hmmm :(