My guess is that this code is never reached.
I raised the Apache LogLevel to debug (see below) but I still have no clue:
[Wed May 17 20:10:27.320020 2023] [proxy_fcgi:debug] [pid 3097337:tid 140540432017152] mod_proxy_fcgi.c(1054): [remote 10.130.51.47:49789] AH01076: url: fcgi://localhost/var/www/wiki/lib/exe/ajax.php proxyname: (null) proxyport: 0, referer: https://webserver/wiki/playground/pagename?do=edit
[Wed May 17 20:10:27.320026 2023] [proxy_fcgi:debug] [pid 3097337:tid 140540432017152] mod_proxy_fcgi.c(1063): [remote 10.130.51.47:49789] AH01078: serving URL fcgi://localhost/var/www/wiki/lib/exe/ajax.php, referer: https://webserver/wiki/playground/pagename?do=edit
[Wed May 17 20:10:27.320032 2023] [proxy:debug] [pid 3097337:tid 140540432017152] proxy_util.c(2596): [remote 10.130.51.47:49789] AH00944: connecting fcgi://localhost/var/www/wiki/lib/exe/ajax.php to localhost:8000, referer: https://webserver/wiki/playground/pagename?do=edit
[Wed May 17 20:10:27.320107 2023] [proxy:debug] [pid 3097337:tid 140540432017152] proxy_util.c(2819): [remote 10.130.51.47:49789] AH00947: connected /var/www/wiki/lib/exe/ajax.php to httpd-UDS:0, referer: https://webserver/wiki/playground/pagename?do=edit
[Wed May 17 20:10:27.320118 2023] [proxy:error] [pid 3097337:tid 140540432017152] (103)Software caused connection abort: [remote 10.130.51.47:49789] AH01095: prefetch request body failed to 0.0.0.0:0 (httpd-UDS) from 10.130.51.47 (), referer: https://webserver/wiki/playground/pagename?do=edit
The last line I interpret as PHP rather than Apache denying the request but I am not sure.
Since it seems to happen after a Cancel and I sadly don't have the knowledge nor time to pursue this any further, I'll leave it as it is.