Write AWK command's result into new CSV file

Assuming that the eight fields of each record are always present, are in the correct order, and do not need further processing to be valid in a CSV file (i.e. no extra quoting or escaping is needed):

sed -n 's/^[^=]*= //p' file | paste -d , - - - - - - - -

This removes any line that does not contain any equal signs followed by space (or lines where the = substring doesn't contain the first equal sign on the line), then strips off any text up to the space after the first equal sign.

It then uses paste to create eight comma-delimited columns of the remaining data.

Testing on a file containing your example data twice:

$ sed -n -e 's/^[^=]*= //p' file | paste -d , - - - - - - - -
"407359687",Interim-Update,3263901190,"PPP3092201SSG0001006b0a55AABODS",1146851,15,"Aug 22 2021 18:55:32 +08",1629630000
"407359687",Interim-Update,3263901190,"PPP3092201SSG0001006b0a55AABODS",1146851,15,"Aug 22 2021 18:55:32 +08",1629630000

Removing any line with Start in the second column (to filter out sections that had Acct-Status-Type = Start in the original data) could be done by piping the result through

awk -F , '$2 != "Start"'

I would start with

awk -F= 'NF==2{printf "%s%s",comma,substr($2,2);comma=","} END {printf "\n" }' source > dest

where

• -F= use = as seprator
• NF==2 select line with 2 fields
• substr($2,2) strip leading space
• source and dest are source and destination files.

if you want to keep you program, you can replace

if (($1=="Acct-Session-Id")&&(start==1))
{wholeLine=wholeLine","$3;}

by

$1 ~ /Acct-Session-Id/ && (start==1) {wholeLine=wholeLine","substr($2,2);}

and remove enclosing { ... } as @berndbausch pointed out.

In the following, I assume your input data is always sorted the right way, i.e. each block from "User-Name" to "Timestamp" has the data you wish to extract in the right order, and "Event-Timestamp" is second to last.

In that case you may just use awk's capability of working on ranges, defined by pattern matches: /start/,/end/.

'BEGIN { FS=" = " }
/User-Name/,/Event-Timestamp/ {printf "%s,",$2}
/ Timestamp/ {print $2}'

Note that the pattern match "/ Timestamp/" needs a space in the beginning for not matching "Event-Timestamp", too. Other appearances of the matched patterns are not considered and might break the script.

Sample input:

Sun Aug 22 19:00:00 2021
        User-Name = "407359687"
        Acct-Status-Type = Interim-Update
        Acct-Output-Octets = 3263901190
        Acct-Session-Id = "PPP3092201SSG0001006b0a55AABODS"
        Acct-Session-Time = 1146851
        Acct-Output-Gigawords = 15
        Event-Timestamp = "Aug 22 2021 18:55:32 +08"
        Timestamp = 1629630000
RANDOM ANNOYANCE
AND AN EMPTY LINE

Sun Aug 22 19:00:00 2021
        User-Name = "407359687"
        Acct-Status-Type = Interim-Update
        Acct-Output-Octets = 3263901190
        Acct-Session-Id = "PPP3092201SSG0001006b0a55AABODS"
        Acct-Session-Time = 1146851
        Acct-Output-Gigawords = 15
        Event-Timestamp = "Aug 22 2021 18:55:32 +08"
        Timestamp = 1629630000

sample output:

"407359687",Interim-Update,3263901190,"PPP3092201SSG0001006b0a55AABODS",1146851,15,"Aug 22 2021 18:55:32 +08",1629630000
"407359687",Interim-Update,3263901190,"PPP3092201SSG0001006b0a55AABODS",1146851,15,"Aug 22 2021 18:55:32 +08",1629630000

EDIT:

Following the requirement for excluding "Acct-Status-Type = Start", I'd suggest running a second implementation of awk removing such lines:

awk ' ...above code...' file | awk -F, '$2!="Start"'

Using Raku (formerly known as Perl_6)

raku -e 'my @array; for lines() {@array.push($_) if /User\-Name/ fff /<!after Event\-> Timestamp/}; 
         @array>>.split(/^^ .+? " = "/, :skip-empty).batch(8).map(*.join(",")).join("\n").put;'

Sample input (after @FelixJN):

Sun Aug 22 19:00:00 2021
        User-Name = "407359687"
        Acct-Status-Type = Interim-Update
        Acct-Output-Octets = 3263901190
        Acct-Session-Id = "PPP3092201SSG0001006b0a55AABODS"
        Acct-Session-Time = 1146851
        Acct-Output-Gigawords = 15
        Event-Timestamp = "Aug 22 2021 18:55:32 +08"
        Timestamp = 1629630000
RANDOM ANNOYANCE
AND AN EMPTY LINE

Sun Aug 22 19:00:00 2021
        User-Name = "407359687"
        Acct-Status-Type = Interim-Update
        Acct-Output-Octets = 3263901190
        Acct-Session-Id = "PPP3092201SSG0001006b0a55AABODS"
        Acct-Session-Time = 1146851
        Acct-Output-Gigawords = 15
        Event-Timestamp = "Aug 22 2021 18:55:32 +08"
        Timestamp = 1629630000

sample output:

"407359687",Start,3263901190,"PPP3092201SSG0001006b0a55AABODS",1146851,15,"Aug 22 2021 18:55:32 +08",1629630000
"407359687",Interim-Update,3263901190,"PPP3092201SSG0001006b0a55AABODS",1146851,15,"Aug 22 2021 18:55:32 +08",1629630000

While I recognize the OP asked for an awk solution, the Perl family of languages is famous for text processing. The 'one-liner' Raku code above uses the fff "flip-flop" operator to capture text between two sentinel lines, the first matching the "User-Name" line and the second matching the "Timestamp" line. A negative lookbehind <!after Event\-> is used to make sure that the regex doesn't recognize the "Event-Timestamp" line by mistake.

The selected lines are pushed onto @array and then split() is used to get rid of everything to the left of the desired values. Records are batch()-ed in groups (columns) of 8, and a map() call is used to join() values with commas. Successive record rows are joined by newlines.

Removing any CSV rows with Start in the second column can be accomplished by piping the above one-liner through the following:

raku -ne '.put unless .split(",")[1] eq "Start";'

This is a good place to start if CSV is going to be a major part of your computing life. Raku has a number of CSV modules to help you with more complicated CSV cases.

https://modules.raku.org/search/?q=CSV
https://raku.org/