It looks to me that’s the one in the guide on the official website of AdGuard DNS.
Isn’t it dns.adguard-dns.com?
I’m using Linux Mint with the Cinnamon desktop on a Thinkpad older than yours, and everything works fine for me. I’ve seen somebody saying that the Xfce edition is slow for them, but maybe the MATE one is lightweight enough for you.
It looks to me that’s the one in the guide on the official website of AdGuard DNS.