It is compatible with Nginx+FPM. It won't use the PHP-FPM specific logs (and thus does not impose any specific value from you for the access.format PHP-FPM setting). But it has to figure out where your app's error log is.
The wpdb logic is an addon and only triggers if wpdb is found. Phptop might still be useful in the general case to quickly and cheaply find CPU hotspots.
Nowadays it would be necessary to also show the various Curl/API calls because they're so omnipresent and impactfull on PHP sites (as wait time and not CPU time)... But AFAIK it's pretty hard to intercept them in a generic way.
"Query" does mean "HTTP request" in the summary. It's reported as "Hits" in the stats. Sorry for the incoherent wording ...
The SQL/wpdb support was added afterwards, and it shows because data is only collected but not used/displayed in the histograms.
Phptop is wayyy simpler and not even comparable to SPX, but you can install it in a few sec, use it 5min, uninstall it, and solve lots of common perf problem. That was my use case (it'as ancient code and I barely use it nowadays).
I'm the author, it's funny this thing pops up now, it was written +15 years ago and is barely maintained (but AFAKI still works).
The metrics collected are close to those from PHP-FPM (CPU user/sys, clock time, peak memory) + the wpdb hook because I had to profile lots of WP.
The most interesting part is the 'phptop' tool itself which actually parse the logs and make some useful histograms.
Its main force I think it's that it's very lightweight (500 lines of Perl, fast and efficient regexes), works everywhere (very old Perl will do), and gives results instantly. My usecase used to be : apt install phptop, wait (at least) 1min for data collection, get useful histogram. It's also obviously very easy to uninstall.
It does pollute the error log, but it's the most simple and universal data sink I could think of, and well it's a hack in the end.