Failed CORS: null vs 192.168.1.9, , dns.somesecretname.nl, pi.hole, localhost

Anyone that can tell me what to look for regarding the CORS error?
The other forum entries about it did not solve it for me.

I succeeded in a clean/fresh re-install.
The new debug token is: https://tricorder.pi-hole.net/xzx9ze8s5x
The 'modifications' that I presumably made did not make a difference.
I followed: https://docs.pi-hole.net/guides/nginx-configuration/

Apparently nobody uses this with nginx, php7.3-fpm on debian 10. Color me flabbergasted.