Server can't find pi.hole: NXDOMAIN

I have installed Pi-hole on my Raspberry Pi for some time now. On my dashboard, I see the number of blocked queries increasing (blocking percentage 30%). If that Raspberry Pi goes down, I have no internet (wifi) on all my devices anymore. Also, certain (sponsored) sites are blocked. Based on this, I think Pi-hole is working well.

Now I'm trying to test if it works with the command "nslookup pi.hole" and then I get:

Server: 1.1.1.1
Address: 1.1.1.1#53

** server can't find pi.hole: NXDOMAIN

That doesn't seem right to me. So now I doubt whether Pi-Hole is working properly.

Is my conclusion correct, and if so, does anyone have any tips for me?

Info Pi-Hole:
Pi-hole v5.7
FTL v5.12
Web Interface v5.9