In modern home labs and small networks, it is common to operate multiple VLANs or subnets routed through a single gateway. While Pi-hole supports acting as a DHCP server, it is currently limited to a single DHCP scope and does not support multiple scopes per instance, which restricts its usability in segmented network environments. Can Pi-hole be enhanced to support multiple DHCP scopes?
If DNSMasqd which is used for FTLDNS can do it then you can do it by adding the right config lines/options to the right config files.
Since the release of Pi-Hole v6 it even binds by default to all my VLAN Interfaces so adding the DHCP Scopes to those is now even less effort than it was before! 
I don’t use Pi-Hole for DHCP but I am 100% sure it can be done after reading a bit of documentation @ Man page of DNSMASQ
Indeed Pi-hole already supports this by dnsmasq tagging the network interface(s):
You can add those three dnsmasq directives per interface via the webGUI:
Settings > System > flip Basic to Expert > All Settings > Miscellaneous > misc.dnsmasq_lines
Or use the misc.etc_dnsmasq_d setting on that same page.
I hit this exact wall running a few VLANs at home and ended up building a small self-hosted tool to work around it rather than wait on core support: pihole-fleet-manager. It layers extra DHCP scopes on top of Pi-hole's single built-in one — subnet, range, gateway, lease time, static reservations, even per-VLAN conditional forwarding — and renders them as a dnsmasq.d snippet pushed to every node over SSH, with pre-flight validation so a bad config can't fan out to the whole fleet. Not a replacement for native support, but it's been solid for my 3-node cluster if anyone wants a stopgap.