This platform is one of the many that I use and configurations are all working as designed, except this raspberry. It used to work, but the SD-card broke down.
I used the installation script and everything looks OK afterwards, but I don’t see the virtual zerotier network adapter listed when requested. When requesting the status of zerotier running I get the following error: ERROR: unable to configure virtual network port: could not open TUN/TAP device: Is a directory
This tun device in indeed not original available, but even if created and chmod 0666, I still have the issue.
Any help is very welcome 
OS:
cat /etc/os-release
PRETTY_NAME=“Raspbian GNU/Linux 11 (bullseye)”
NAME=“Raspbian GNU/Linux”
VERSION_ID=“11”
VERSION=“11 (bullseye)”
VERSION_CODENAME=bullseye
ID=raspbian
ID_LIKE=debian
root@raspberrypi:~# curl -s | sudo bash
*** ZeroTier Service Quick Install for Unix-like Systems
*** Tested OSes / distributions:
*** MacOS (10.13+) (just installs ZeroTier One.pkg)
*** Debian Linux (7+)
*** RedHat/CentOS Linux (6+)
*** Fedora Linux (16+)
*** SuSE Linux (12+)
*** Mint Linux (18+)
*** Supported architectures vary by OS / distribution. We try to support
*** every system architecture supported by the target.
*** Please report problems to contact@zerotier.com and we will try to fix.
*** Detecting Linux Distribution
*** Found Debian, creating /etc/apt/sources.list.d/zerotier.list
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
OK
*** Installing zerotier-one package…
Hit:1 h…p://download.zerotier.com/debian/bullseye bullseye InRelease
Hit:2 h…p://raspbian.raspberrypi.org/raspbian bullseye InRelease
Hit:3 h…p://archive.raspberrypi.org/debian bullseye InRelease
Reading package lists… Done
Reading package lists… Done
Building dependency tree… Done
Reading state information… Done
The following NEW packages will be installed:
zerotier-one
0 upgraded, 1 newly installed, 0 to remove and 49 not upgraded.
Need to get 0 B/793 kB of archives.
After this operation, 2,611 kB of additional disk space will be used.
Selecting previously unselected package zerotier-one.
(Reading database … 47217 files and directories currently installed.)
Preparing to unpack …/zerotier-one_1.10.1_armhf.deb …
Unpacking zerotier-one (1.10.1) …
Setting up zerotier-one (1.10.1) …
Processing triggers for man-db (2.9.4-2) …
*** Enabling and starting ZeroTier service…
*** Waiting for identity generation…
*** Success! You are ZeroTier address [ … ]
root@raspberrypi:~# zerotier-cli join 1…aaaccc.
500 join {}
root@raspberrypi:~# systemctl status zerotier-one
● zerotier-one.service - ZeroTier One
Loaded: loaded (/lib/systemd/system/zerotier-one.service; enabled; vendor preset: enabled)
Active: active (running) since Sat 2022-10-22 09:16:39 CEST; 7min ago
Main PID: 28549 (zerotier-one)
Tasks: 4 (limit: 877)
CPU: 9.653s
CGroup: /system.slice/zerotier-one.service
└─28549 /usr/sbin/zerotier-one
Oct 22 09:23:10 raspberrypi zerotier-one[28549]: connect: Connection refused
Oct 22 09:23:10 raspberrypi zerotier-one[28549]: connect: Connection refused
Oct 22 09:23:10 raspberrypi zerotier-one[28549]: connect: Connection refused
Oct 22 09:23:10 raspberrypi zerotier-one[28549]: connect: Connection refused
Oct 22 09:23:10 raspberrypi zerotier-one[28549]: connect: Connection refused
Oct 22 09:23:10 raspberrypi zerotier-one[28549]: connect: Connection refused
Oct 22 09:23:10 raspberrypi zerotier-one[28549]: connect: Connection refused
Oct 22 09:23:10 raspberrypi zerotier-one[28549]: connect: Connection refused
Oct 22 09:23:10 raspberrypi zerotier-one[28549]: connect: Connection refused
Oct 22 09:23:25 raspberrypi zerotier-one[28549]: ERROR: unable to configure virtual network port: could not open TUN/TAP device: Is a directory
Check if /dev/net/tun exists → no.
Created and chmod 0666 tun according the openvpn manual found online
ifconfig
enxb827eb5b74f3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.3 netmask 255.255.255.0 broadcast 192.168.1.255
ether b8:27:eb:5b:74:f3 txqueuelen 1000 (Ethernet)
RX packets 472625 bytes 70892307 (67.6 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 424286 bytes 49523983 (47.2 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
loop txqueuelen 1000 (Local Loopback)
RX packets 4568 bytes 312436 (305.1 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 4568 bytes 312436 (305.1 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0