I started with a fresh installation of the Raspberry Pi OS on a Raspberry Pi 4. I followed your instructions, to the letter.
There does seem to be one omission in the instructions. They say to enable the owserver service, but they don't say to start it. So after enabling the service, I rebooted. Presumably that would start the service. Also, since the instructions say to enable /mnt/1wire in the OWFS section of /etc/owfs.conf, it appears to be unnecessary to run the owfs command manually, as shown at the end of the instructions.
Anyhoo, it still doesn't work. I see none of my devices listed when I run the example Python program. Also, if I do "i2cdetect -y 1" I don't see the 1wire device at address 18, as I would expect.
So, wow, a lot of work for nothing.
Another bit of info. After I ran the Python program, I used journalctl -u owserver and saw the following. It would appear that the error message was logged at the moment the Python program tried to enumerate the 1wire devices.
root@raspberrypi:/home/pi# journalctl -u owserver -n 10
-- Logs begin at Sun 2021-05-02 09:35:22 EDT, end at Sun 2021-05-02 09:36:20 EDT. --
May 02 09:35:26 raspberrypi systemd: Starting Backend server for 1-wire control...
May 02 09:35:26 raspberrypi owserver: DEFAULT: ow_opt.c:(670) systemd mode -- ignore 'p' option
May 02 09:35:27 raspberrypi systemd: Started Backend server for 1-wire control.
May 02 09:36:18 raspberrypi owserver: DEFAULT: ow_reconnect.c:(69) Failed to reconnect DS2482-100 bus master!