There is a brilliant report named "Dormant user security accounts" found under the menu: System administration > Security
Unfortunately this report is hidden under the "Public sector" license key. So for us who are not using "Public sector" this report is invisible.
I would suggest to change the license key to the same license key as the form "Users".



https://alexdmeyer.com/2019/01/07/dormant-user-account-reporting-in-d365fo-pu21-8-1/