This is my setting when assigning static IPs to KVM guests using DHCP in Proxmox. Currently I have 1 public IP and 2 failover IP (both failover IP has MAC address attached).

Install the DHCP server :

apt install isc-dhcp-server

Edit the config:

vi /etc/default/isc-dhcp-server

# Add below lines. The default bridge is vmbr0.
INTERFACES="vmbr0"

Modify the /etc/dhcp/dhcpd.conf. Example:

subnet 0.0.0.0 netmask 0.0.0.0 {
authoritative;
default-lease-time 21600000;
max-lease-time 432000000;
}

# Bind IP by MAC
host VM1 {
hardware ethernet 52:54:xx:xx:xx:x1;
option routers 62.xxx.xxx.1;
option subnet-mask 255.255.255.255;
fixed-address xxx.xxx.xxx.114;
option domain-name-servers 8.8.8.8,8.8.4.4;  
}

host VM2 {
hardware ethernet 52:54:xx:xx:xx:x2;
option routers 62.xxx.xxx.1;
option subnet-mask 255.255.255.255;
fixed-address xxx.xxx.xxx.115;
option domain-name-servers 8.8.8.8,8.8.4.4;  
}

Make sure the dhcp server running after reboot:

systemctl enable isc-dhcp-server
reboot

Later when creating the VM we just need to specify the MAC address for specific IP and than just use DHCP to get the assigned IP.