For many Years I was using a wlan SSID containing a backslash with no problems.
While trying the current Armbian_community_26.11.0-trunk.62_Bananapim2plus_trixie_current_6.18.54_minimal.img.xz the network wlan0 would not connect.

Connecting to the guest wlan of the same router worked.

I could trace it to the backslash in the SSID which "netplan try" complained about.

Escaping that with a additional backslash made "netplan try" accept it, but the connection did not work, the interface wlan0 remained in status "state DOWN".

Changing the SSID (removing that single backslash) made it working.

I did not find something that prohibits the backslash used in the name of the SSID, so I'm unsure.

What does the command 'sudo netplan --debug generate' return?

here is the output for different tries:

 

 

------------------------------------------------------------------------
with just one \

@bananapim2plus:~$ sudo netplan --debug generate
DEBUG:command generate: running ['/usr/libexec/netplan/generate']
** (generate:1533): DEBUG: 10:01:53.319: starting new processing pass
/etc/netplan/armbian.yaml:10:17: Invalid YAML: found unknown escape character:
        "*****cq\2or*****":
                ^ (this points to the \ here wrong due to the type of characters)
mschz@bananapim2plus:~$ 
------------------------------------------------------------------------
with \\ in order to escape the \

user@bananapim2plus:~$ sudo netplan --debug generate
DEBUG:command generate: running ['/usr/libexec/netplan/generate']
** (generate:1465): DEBUG: 09:56:57.191: starting new processing pass
-- from /etc/netplan/30-wifis-dhcp.yaml
** (generate:1465): DEBUG: 09:56:57.192: wlan0: adding wifi AP '2{*****cq\2or*****'
** (generate:1465): DEBUG: 09:56:57.193: starting new processing pass
-- from /etc/netplan/armbian.yaml
** (generate:1465): DEBUG: 09:56:57.193: wlan0: adding wifi AP '2{*****cq\2or*****'
** (generate:1465): DEBUG: 09:56:57.193: We have some netdefs, pass them through a final round of validation
** (generate:1465): DEBUG: 09:56:57.193: wlan0: setting default backend to 1
** (generate:1465): DEBUG: 09:56:57.193: Configuration is valid
** (generate:1465): DEBUG: 09:56:57.195: Generating output files..
** (generate:1465): DEBUG: 09:56:57.195: Creating wpa_supplicant config
** (generate:1465): DEBUG: 09:56:57.195: wlan0: Creating wpa_supplicant configuration file run/netplan/wpa-wlan0.conf
** (generate:1465): DEBUG: 09:56:57.196: Creating wpa_supplicant unit /run/systemd/system/netplan-wpa-wlan0.service
** (generate:1465): DEBUG: 09:56:57.223: Creating wpa_supplicant service enablement link /run/systemd/system/systemd-networkd.service.wants/netplan-wpa-wlan0.service
** (generate:1465): DEBUG: 09:56:57.224: Open vSwitch: definition wlan0 is not for us (backend 1)
** (generate:1465): DEBUG: 09:56:57.224: NetworkManager: definition wlan0 is not for us (backend 1)
user@bananapim2plus:~$ 

user@bananapim2plus:~$ sudo cat /run/netplan/wpa-wlan0.conf 
ctrl_interface=/run/wpa_supplicant

network={
  ssid=P"*****cq\2or*****"
  key_mgmt=WPA-PSK WPA-PSK-SHA256 SAE
  ieee80211w=1
  psk="~~~~~"
}
user@bananapim2plus:~$ 
------------------------------------------------------------------------
without any \

user@bananapim2plus:~$ sudo netplan --debug generate
DEBUG:command generate: running ['/usr/libexec/netplan/generate']
** (generate:1745): DEBUG: 10:08:55.390: starting new processing pass
** (generate:1745): DEBUG: 10:08:55.391: wlan0: adding wifi AP '*****cq2or*****'
** (generate:1745): DEBUG: 10:08:55.392: starting new processing pass
** (generate:1745): DEBUG: 10:08:55.392: wlan0: adding wifi AP '*****cq2or*****'
** (generate:1745): DEBUG: 10:08:55.392: We have some netdefs, pass them through a final round of validation
** (generate:1745): DEBUG: 10:08:55.392: wlan0: setting default backend to 1
** (generate:1745): DEBUG: 10:08:55.393: Configuration is valid
** (generate:1745): DEBUG: 10:08:55.394: Generating output files..
** (generate:1745): DEBUG: 10:08:55.394: Creating wpa_supplicant config
** (generate:1745): DEBUG: 10:08:55.394: wlan0: Creating wpa_supplicant configuration file run/netplan/wpa-wlan0.conf
** (generate:1745): DEBUG: 10:08:55.395: Creating wpa_supplicant unit /run/systemd/system/netplan-wpa-wlan0.service
** (generate:1745): DEBUG: 10:08:55.422: Creating wpa_supplicant service enablement link /run/systemd/system/systemd-networkd.service.wants/netplan-wpa-wlan0.service
** (generate:1745): DEBUG: 10:08:55.423: Open vSwitch: definition wlan0 is not for us (backend 1)
** (generate:1745): DEBUG: 10:08:55.423: NetworkManager: definition wlan0 is not for us (backend 1)
user@bananapim2plus:~$ sudo cat /run/netplan/wpa-wlan0.conf 
ctrl_interface=/run/wpa_supplicant

network={
  ssid=P"*****cq2or*****"
  key_mgmt=WPA-PSK
  psk="~~~~~"
}
user@bananapim2plus:~$

See if quoting the password inside /etc/netplan/armbian.yaml (or if it's inside /etc/netplan/30-wifis-dhcp.yaml) works.

 

8 hours ago, ttnp said:

ssid=P"*****cq2or*****"

 

That looks strange to me (wpa_supplicant), P"yadayada" instead of quoting the whole sting.

Also to me it looks strange, but it works (in the configuration without the backslash)