At least in my case, I once caught Slack.exe on windows using 40GB of RAM. (My machine had 32GB, so you can imagine how well things were running.) The allocated space seemed to have mostly been zeroes since the Windows Kernel was able to compress a bunch of the pages to avoid running out, but it was putting so much strain on things that audio playback was dropping out.

I've changed jobs since so I don't have access to the tickets but I remember it being close to 20GB.