Steps to reproduce:

1. Install PostgreSQL 13 primary and standby instance, add them with agent2 template.
2. Navigate to items of standby host.
3. Change filter to not supported.
4. You will see PostgreSQL by Zabbix agent 2: PostgreSQL: Get WAL
   not supported because it gives the error Cannot fetch data: ERROR: recovery is in progress (SQLSTATE 55000)

Or from the standby host with zabbix agent2:

$ zabbix_get -s 127.0.0.1 -k 'pgsql.wal.stat["<PG.URI>","<PG.USER>","<PG.PASSWORD>"]'
ZBX_NOTSUPPORTED: Cannot fetch data: ERROR: recovery is in progress (SQLSTATE 55000).

Result:
See screenshot...

Expected:
In the template "PostgreSQL by user parameters" the item works correctly because recovery state is checked before query.