Bluetooth NAP Network on RPi4 - package: bluez-utils

bt-agent.service

# /etc/systemd/system/bt-agent.service

[Unit]
Description=Bluetooth Auth Agent

[Service]
ExecStart=/usr/bin/bt-agent -c NoInputNoOutput
Type=simple

[Install]
WantedBy=multi-user.target

bt-network.service

# /etc/systemd/system/bt-network.service

[Unit]
Description=Bluetooth NEP PAN
After=pan0.network

[Service]
ExecStart=/usr/bin/bt-network -s nap pan0
Type=idle

[Install]
WantedBy=multi-user.target

pan0.netdev

# /etc/systemd/network/pan0.netdev

[NetDev]
Name=pan0
Kind=bridge

pan0.network

# /etc/systemd/network/pan0.network

[Match]
Name=pan0

[Network]
Address=192.168.2.1/24
DHCPServer=yes

I love this setup, and i made a small minor tweak to bt-agent.service, that gives you the command to use on the client, lol.
if you happen to work from a terminal client that allows copy and paste, otherwise you would just type it out as listed.

ExecStartPost=sh -c 'printf "%%s\n" "clients use: sudo bt-network -C $( bt-adapter -l | sed -rn "s/.?(([[:xdigit:]]{2}:){5}[[:xdigit:]]{2})./\1/p" ) nap"'