The following bug has been logged on the website:
Bug reference: 17415
Logged by: Daniel Polski
Email address: danielpolski(at)gmail(dot)com
PostgreSQL version: 14.2
Operating system: Linux
Description:
SELECT set_config('_foo.bar', 'foo', FALSE);
ERROR: invalid configuration parameter name "_foo.bar"
DETAIL: Custom parameter names must be two or more simple identifiers
separated by dots.
SQL state: 42602
(Works in 13.5-2)