This has been asked before, see e.g.
Wifi hotspot not suppling ip & kills FTLDNS.
NetworkManager is able to start dnsmasq processes as required.
NM configures them via configuration files from /etc/NetworkManager/dnsmasq-shared.d (for its hotspot service) and /etc/NetworkManager/dnsmasq.d/ (for its DNS service).
So for NM's dnsmasq DHCP service and pihole-FTL's DNS service to coexist, you 'd have to make sure that neither one uses the ports of the other.
If you want Pi-hole to handle DNS, try adding port=0 to NM's dnsmasq config files to disable NM's DNS functionality and only leave DHCP.