Is there a list of GOG games that don't work on Windows 10, so that I can prioritize them on my backlog before upgrading from W7?

You could try using this: http://www.an-ovel.com/pages/magog.php

I'm not sure if it's still updated, but it allows for a more robust search of the catalogue.

I'm pretty sure there used to be GOGmixes for titles that weren't supported on Win 7/8/10, but I don't know how up-to-date they were kept by their creators even well before the GOGmix infrastructure started to sport the technical problems that contributed to that feature being killed off (and it's not as if none of those games would've been updated to be able to be supported on later OSes since then). You'd have to find the archived versions yourself, too.

You could use MaGog, but its usefulness has been purposely hobbled by the misapplied idealism of its creator (games added to the store after a certain arbitrary date are not included in the database as a form of protest). I don't know if sites like IsThereAnyDeal have ways to filter games that aren't supported on a particular OS version, but if so, one of those would probably be your best bet.

How do I get that to search for titles which are literally Broken in Windows 10?

I don't think you could get that. But you can search for games that don't list windows 10 as a supported OS by going to the filters heading and selecting a filter for Operating systems.

I know it's not exactly what you were looking for. It's just the closest thing that I can offer.

I have yet to find a single game which doesn’t work on windows 10 (some with tweaking) outside of call of juarez 1/2, and even that seems compatible from gog. In the unlikely event you do find one, check the games forum and pcgamingwiki as there will be a mod or patch or other fix. And if all that fails, dual boot or virtual image.

Sadly dont know any resource which precisely states which games are definitely broken under win 10 under any circumstances.
But have to agree with nightcraw1er from my personal experiences as well.
Did not have any game in my library yet which refused to work categorically under win 10 (there was like 2-3 games do which required manual workarrounds which were not originally implemented by gog)

Any list mentioning broken Win10 compability should also state the version as the are some games wich broke with updates.

This isn't that easy.....Win10 updates so much that some games might work one moment and after an update they might not. Post 6 here is a good suggestion, and should work well for you. :)

=======================Really? That's messed up.....if one makes a tool to help others by listing info on games sold they shouldn't purposefully hobble it due to personal tastes/bias.

Games that GOG does not mark as working on Windows 10:
[url=]http://www.an-ovel.com/cgi-bin/magog.cgi?ver=1000&scp=gdspuiolnc&dsp=ipgfsorlcmbahATSWv&ord=&flt=onn~w10~&opt=nr[/url]

Great filter, thanks! Even if there are ways to get them to work, it's a good starting point :)