The term 'demonetization' can be misleading. It's the creator who is demonetized on a demonetized video or channel. YouTube still often shows ads on such videos, it just keeps all the money instead of 45% of it.
The only ad they show is a regular display and on the right hand side out of the video frame, and as far as I know revenue from that ad is never given to the creator anyway.
It may depend on what country you're in or if you're on mobile or not. I wouldn't know for certain, I'm a uBO/NewPipe man.
I may be wrong but I don't see evidence that Youtube continues showing ads on demonetized content like these explicit Ukraine war videos. The reason is that the advertisers who pay money to Google don't want their brands associated with certain types of lurid content. (See Adpocalypse: https://www.google.com/search?q=biggest+advertisers+abandon+...)
So, Google is being extra strict with ads on these videos to avoid an angry call from a giant advertiser like Proctor & Gamble complaining, "Why are you showing my dish soap ads on a video of a naked guy getting killed while pooping?!?" (E.g.: https://www.tubefilter.com/2018/04/20/pg-resumes-youtube-spe...)
There also may be some confusion about some videos with ads and creators not getting the money: the creator has not been accepted into the Partner Program for revenue sharing. Yes, in those cases, the creators are not getting ad $$$ -- even for safe advertiser-friendly videos.
But these Ukraine demonetization videos seem more like not repeating the Adpocalypse debacle and Google will not run ads on them.
Of course, Google/Youtube's system isn't perfect so there will be false-positives. Will there be indecent videos that Google improperly display ads on? Yes. Will there also be high-quality channels that got unfairly demonetized even if advertisers would have no objection to their content? Yes.
You're quite right that there's some confusion between Partner Program eligibility and demonetization proper. This Ukraine war creator actually talks about being removed from the Partner Program in the video linked in this post.
† It was a deepfake of the current Israeli Prime Minister explaining why I should vote for Shas, a party of which he is most definitely not a member. Not relevant to this issue but too crazy not to mention.