I had been using AdGuard DNS. All of a sudden, my work laptop was acting weird. While other apps were connecting, Teams wasn’t connecting.
I ran DNS leak test and discovered that AdGuard DNS was resolving to Canadian IP addresses. I changed from AdGuard to Cloudfare DNS (1.1.1.1) and Teams been running fine since. Is this safe DNS to use and doesn’t have any non-US servers?
Hope I didn’t raise any flags with my employer.
All big DNS providers use Anycast so the fastest server will respond - can be, theoretically, in any country.
Microsoft could services aren't fun to whitelist. It is not one service, for authentication there are other services involved.
On topic: If you want to use AGH with MS cloud services I recommend to use a whitelist. For example: AdGuard-Home-Whitelist/Modules/Organizations/microsoft_whitelist.txt at main · hl2guide/AdGuard-Home-Whitelist · GitHub
Off topic: But personally I would recommend to avoid MS cloud services 
I use AdGuard DNS (and Mullvad VPN) with all MS services totally fine, btw.
I used nextdns over TLS, $2 per month, it's worth. Full protection - full control.