I use two Technitium DNS servers, the primary server runs in a container under Proxmox and the secondary as a failover on a Pi4. I only use Pihole for a handful of clients (mobile phone, FireTV etc.) these are assigned the DNS address from PiHole via DHCP, all other devices use the Technitium DNS directly. As internal domains I use the scheme “host.in.lan” and all devices (except servers) get their IP via DHCP (the Technitium DNS server also has this built in) and a DNS entry is automatically created for them via DDNS