parse colon separated value pairs

The script that you linked to is extremely inefficient - you're doing a lot of useless pre-processing...
Use nmcli in --terse mode since, per the manual, "this mode is designed and suitable for computer (script) processing", specify the desired fields and pipe the output to jq -sR e.g.

printf '%s' "$(nmcli -f ssid,mode,chan,rate,signal,bars,security -t dev wifi)" | \
jq -sR 'split("\n") | map(split(":")) | map({"network": .[0],
                                             "mode": .[1],
                                             "channel": .[2],
                                             "rate": .[3],
                                             "signal": .[4],
                                             "bars": .[5],
                                             "security": .[6]})'

This GNU sed code isn't jq, (it isn't a complex conversion), but it seems to work well enough, (even the bars come out OK):

nmcli --mode multiline dev wifi | 
sed    '/^*/! {s/^[A-Z]*/\L&/
               s/ssid/network/
               s/: */": "/
               s/$/"/
               {/^sec/!s/$/,/}
               s/^/\t"/}
        1     s/^\*.*/[{/
        /^\*/ s/.*/},\n{/
        $  {p;s/.*/}]/}'

Easier to read standalone pcsvp.sed script, (save to file, then run chmod +x pcsvp.sed):

#!/bin/sed -f
# Text lines (the non "*:" lines.)
/^*/! {s/^[A-Z]*/\L&/
       s/ssid/network/
       s/: */": "/
       s/$/"/
       {/^sec/!s/$/,/}
       s/^/\t"/}

# First JSON line
1     s/^\*.*/[{/

# Middle JSON lines.  If a line begins with a '*'...
/^\*/ s/.*/},\n{/

# Last line, close up the JSON.
$     {p;s/.*/}]/}

To run that do:

nmcli --mode multiline dev wifi | ./pcsvp.sed

---

Note: Since there are doubts about the input file, I've opted to use nmcli for input instead. At my location this shows about 50 networks, which makes the resulting output too long to quote here.

If the input sample typo is corrected, ./pcsvp.sed input.txt outputs:

[{
    "network": "VIDEOTRON2255",
    "mode": "Infra",
    "chan": "11",
    "rate": "54 Mbit/s",
    "signal": "69",
    "bars": "▂▄▆_",
    "security": "WPA1 WPA2"
},
{
    "network": "VIDEOTRON2947",
    "mode": "Infra",
    "chan": "6",
    "rate": "54 Mbit/s",
    "signal": "49",
    "bars": "▂▄__",
    "security": "WEP"
}]