Hi, Tonybau! I'm delighted to see you again in the Forum's discussion boards after quite a long while, and thanks for your felicitations on the Forum's having existed and survived for over a decade now.
Of course you're right in having always used "taken care of" instead of "taken cared of," so the grammatically correct construction for the sentence you presented is as follows: "The serious Covid19 cases were taken care of at the ICU."
I wrote an essay about this usage way back on January 18, 2018 entitled "The disturbing high incidence of the faulty 'taken cared of' usage." (http://josecarilloforum.com/forum/index.php?topic=6762.0) I pointed out that it's when people use “take care of” in the past participle form that the problem often arises. Simply click the indicated link to read it.
(http://josecarilloforum.com/imgs/taken-care-of_proper-usage-1A1.png)
You can actually access and browse most of my English-usage essays that have been published in The Manila Times from 2013 until the present day by clicking this link to the Forum's "2013-2020 'English Plain and Simple' columns in The Manila Times." (http://josecarilloforum.com/forum/index.php?board=23.0) You can surely further polish your English by reading the essays during your rest breaks from your work helping patients fight off Covid-19.
Good luck, Tonybau, and keep yourself safe always despite your close encounters with that extremely nasty virus!