[neomaslov]

Yes, it helped! I've added my local DNS server running on 192.168.31.50, where PiHole is located to namservers declaration in /etc/netplan/default.yaml:

Code:

network:
  version: 2
  renderer: NetworkManager
  ethernets:
    end0:
      dhcp4: false
      addresses: [192.168.31.61/24]
      routes:
      - to: default
        via: 192.168.31.1
      nameservers:
        addresses: [192.168.31.50]

Explanation:
192.168.31.61 is a machine where FOSS is running
192.168.31.1 is a router which gives out addresses (DHCP)