Cloudflare is a good choice. I used DNSExit for a while, and also NS1, but settled on Cloudflare. You don’t have to use their proxying, just DNS.

Here’s a Docker Compose for you that will set myhost.mydomain.com to point to your public IP of wherever it is run:

dyndns-cloudflare:
    image: oznu/cloudflare-ddns
    container_name: dyndns-cloudflare
    environment:
      - API_KEY=<key>
      - ZONE=mydomain.com
      - SUBDOMAIN=myhost
      - PROXIED=false
    restart: unless-stopped