This happens when loading the extension (compiling it works without warning nor error):

tmp=# create extension jsquery;
ERROR: could not load library "/think/cs/re/2022-11-DB15_rh7/lib/postgresql/jsquery.so": /think/cs/re/2022-11-DB15_rh7/lib/postgresql/jsquery.so: undefined symbol: pg_atoi

Grepping for pg_atoi in pg 15's sources comes up empty, so it seems this symbol was removed.

Compiling jsquery did not raise any warnings, though.