Dawnsinger: 2FA seems to disable Captchas, which makes sense because it serves the same purpose, only better. So in order to test this, you would first need to disable 2FA for your account.
Ah ok, I didn't realize that. It would certainly explain why I don't seem to get CAPTCHA on GOG. Has the OP disabled 2FA, and if so, why? Convenience over security?
I do recall seeing it in some instances though, maybe when redeeming a code or something? But I don't recall when I've seen it, if ever, during logging in.
Dawnsinger: Logging out (which I always do after use) triggers 2FA every time I try to relog, which is understandable and OK given my setup, I wouldn't expect anything less in fact.
To me it earlier felt that if either your IP address remains the same, OR you have valid login cookies in your browser, 2FA wouldn't be triggered. So if I had logged in successfully, then logged out, cleared the cookies and logged in again, 2FA would not be triggered because my IP address (that GOG sees as my public IP) had remained the same.
On the other hand, if my IP address has changed, but the browser still has valid login cookies, 2FA wouldn't be triggered either.
By yesterday's test, it doesn't seem to be like that anymore. It was actually a bit confusing because first I re-logged in with the same browser where I still had the cookies, IP address had not changed either... yet 2FA was triggered?
But right after that if I logged in with a fresh browser without cookies (still the same IP address), no 2FA?
Dunno, maybe in the second test I had not logged out from my account (even though I had closed the browser) so in GOG's mind I was still logged in from my IP address, and when I logged in from a different browser, GOG accepted it wiithout 2FA because I logged in from the same IP address at which I was still "logged in" in another browser... or something...
I'm going to test it now again, log in with this browser, close the browser, cookies are kept, and I log in with the same browser. So yesterday this triggered 2FA but I was in a different IP address (my workplace), now I am at home, using VPN to my work though so I don't know if that affects how GOG sees me...
EDIT: Tested, and unlike yesterday at my office, 2FA was not triggered this time. The only difference I can think of is the different IP address in these two tests, the same laptop and the same browser. Odd. Or maybe yesterday the cookies were becoming old so GOG figured it wants to renew them or something, hence 2FA...