Got an answer from kitikami from reddit in a post that compares Shkuro with Igors Rausis.
cf Why is there a minimum rating gain when you win?
It appears Shkuro was making tournaments where e'd obviously win where as Rausis was just entering tournaments, of other people, where e's most likely win.
Rausis was entering weak open tournaments that no normal GM would have any interest in and beating amateurs in a handful of classical games, but they at least appeared to be legitimate tournaments.
Shkuro and Kobylianskyi were organizing and directing their own blitz or rapid tournaments where they would play a bunch of random locals over a day or two and then submit their results to FIDE until it pushed them into the top 10 of the World Blitz/Rapid lists. I think there were even some questions about whether they were playing the events at all due to how obscure, poorly organized, and poorly documented they were, but in any case these events had no discernible purpose other than to inflate the rating of the person organizing the event and did not appear to ever have been presented as a serious competition. FIDE's decision to nullify their ratings was as simple as making all these events unrated (which would not have worked for Rausis since other than him farming, the results of those events had legitimate competitive meaning).
Rausis' rating was arguably no more legitimate (and his farming was arguably even less ethical since he was ruining real tournaments for his opponents rather than doing his own vanity thing separately), and you could certainly argue his rating deserved to be handled the same way as the other two. What he was doing was on a smaller scale and exploiting existing tournaments available to anyone, though, whereas the other two appeared to be deliberately manufacturing their own personal rating farms.
Here's a record of a rapid tournament where Kobylianskyi is listed as both Tournament Director and Chief Arbiter and scored 10/10 and a blitz tournament where Shkuro is listed as Tournament Director and scored 33/34.
FIDE's official decision is here: https://doc.fide.com/docs/DOC/2021%20GA/Annex%203.2.1c%20UKRAINIAN%20PLAYERS.%20Final%20Resolutions.pdf
The tournaments were originally rated, but FIDE decided after their investigation to rescind the ratings from all their tournaments within the suspicious time periods. While the investigation was ongoing, it looks like FIDE put them both under a sort of probationary period where the Ukrainian Chess Federation had to get FIDE approval for them enter any rated events, but after FIDE released their decision they were free to enter events as normal again.
It looks like the only thing that happened was FIDE reset their ratings and basically told everyone "don't do this again".