Ah i found it now, thanks. Not sure if that setting was in there in the previous versions.
The #opera-doh flag is no longer working, it seems like #dns-over-https flag is the new flag. For some reason both are still in there.

The latest update broke the DNS over HTTPs setting (opera://flags/#opera-doh) for me.
The option has no effect anymore. Also tried disabling and enabling again.
According to the cloudflare site it is not used anymore. See Cloudflare-Test debug info

It was working fine before, as I just set it up with the previous version but right after the update it broke..