The solution dawned on me today when I saw another attack... I found the attacker by cat'ing /usr/local/apache/domlogs/<server-ip>.log
They're using PMA (of course) but the IP is being reported as 127.0.0.1 because nginx is proxy_pass'ing the connection.
cat /usr/local/apache/domlogs/*.log | grep pma
...
93.86.160.221 - - [11/Dec/2022:23:56:17 -0500] "POST /pma/index.php HTTP/1.1" 200 4800 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:17 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4678 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:18 -0500] "POST /pma/index.php HTTP/1.1" 200 4798 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:18 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4680 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:18 -0500] "POST /pma/index.php HTTP/1.1" 200 4796 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:18 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4678 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:18 -0500] "POST /pma/index.php HTTP/1.1" 200 4800 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:19 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4677 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:19 -0500] "POST /pma/index.php HTTP/1.1" 200 4799 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:19 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4678 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:20 -0500] "POST /pma/index.php HTTP/1.1" 200 4800 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:20 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4678 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:20 -0500] "POST /pma/index.php HTTP/1.1" 200 4800 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:20 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4678 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:20 -0500] "POST /pma/index.php HTTP/1.1" 200 4795 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:21 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4678 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:21 -0500] "POST /pma/index.php HTTP/1.1" 200 4797 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:21 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4678 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:21 -0500] "POST /pma/index.php HTTP/1.1" 200 4800 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:22 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4677 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:22 -0500] "POST /pma/index.php HTTP/1.1" 200 4796 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:22 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4678 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:22 -0500] "POST /pma/index.php HTTP/1.1" 200 4792 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:23 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4680 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:23 -0500] "POST /pma/index.php HTTP/1.1" 200 4800 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:23 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4679 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:23 -0500] "POST /pma/index.php HTTP/1.1" 200 4799 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:23 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4679 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:24 -0500] "POST /pma/index.php HTTP/1.1" 200 4800 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:24 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4680 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:24 -0500] "POST /pma/index.php HTTP/1.1" 200 4800 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:24 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4679 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:25 -0500] "POST /pma/index.php HTTP/1.1" 200 4800 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:25 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4680 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:25 -0500] "POST /pma/index.php HTTP/1.1" 200 4801 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
93.86.160.221 - - [11/Dec/2022:23:56:25 -0500] "GET /pma/index.php?lang=en HTTP/1.1" 200 4678 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36"
...