Your question is about networking in general, not about Pi-hole.
You should consider to also consult documentation and support for your chosen OS and network management tool.
That said, I'll just add my two cents to the answers anyway, and finish that with some generic information about what Pi-hole requires.
I guess whatever works also is correct for you.
deHakkelaar is right to point out that you should consider your OS's respective network manager - not so much because /etc/network/interfaces.d/
won't work anymore, but more to avoid unexplicable behaviour or outright conflicts with your system's preferred network management tool.
Debian introduced alternative ways for network configuraton when they adopted systemd (that was way back with Debian Jessie, I think). It doesn't help that not all Debian-based distributions use the same, and it only adds to the confusion that bits of older documentation and recommendation are still floating around everywhere on the net.
For Debian itself, in addition to the docs NGr linked, you'd also find documentation on the systemd-networkd/NetworkManager way of network configuration on systems with or without a GUI from Debian at Chapter 5. Network setup, with a list of appropriate tools.
In general, your hosting machine requires a stable IP address to run Pi-hole, independently of how you actually ensure that.
You don't necessarily have to manually configure a static IP address on-device (by whichever OS and network tools you see fit).
You could also opt to configure a DHCP lease reservation (aka fixed or static IP address) for your Pi-hole host's MAC address in your router.
While either approach is sufficient, a static on-device IP would be preferable if you'd plan to run Pi-hole as your DHCP server.