This Version Allow run as nobody AND ports below 1024

/etc/systemd/system/frps.service

Systems that has AmbientCapabilities support (usually kernel >= linux4.3)

[Unit]
Description=FRP Server Daemon

[Service]
Type=simple
AmbientCapabilities=CAP_NET_BIND_SERVICE
ExecStart=/opt/bin/frps -c /opt/etc/frps.ini
Restart=always
RestartSec=2s
User=nobody
LimitNOFILE=infinity

[Install]
WantedBy=multi-user.target

Systems that without AmbientCapabilities support,You need apt install libcap2-bin then

[Unit]
Description=FRP Server Daemon

[Service]
Type=simple
ExecStartPre=-/usr/sbin/setcap cap_net_bind_service=+ep /opt/bin/frps
ExecStart=/opt/bin/frps -c /opt/etc/frps.ini
Restart=always
RestartSec=2s
User=nobody
PermissionsStartOnly=true
LimitNOFILE=infinity

[Install]
WantedBy=multi-user.target

/etc/systemd/system/frpc.service

[Unit]
Description=FRP Client Daemon
After=network.target
Wants=network.target

[Service]
Type=simple
ExecStart=/opt/bin/frpc -c /opt/etc/frpc.ini
Restart=always
RestartSec=20s
User=nobody
LimitNOFILE=infinity

[Install]
WantedBy=multi-user.target

Config

systemctl daemon-reload
systemctl enable frpc
systemctl status frpc
systemctl enable frps
systemctl status frps