Configure DNSOverTLS with systemd-resolved - see description
When I filled in the DNS field, I put in the port number (:853). This is a mistake, do not specify the port. You will also need to set your dns (through NetworkManager) to the same server to avoid dns leakage. This can be done through the settings of gnome/plasma.
My setup is with NetworkManager, you can also use systemd-networkd. This setup does not work with Dns-over-https yet