apologies for the misunderstanding, the correct file is

/var/log/mongodb/mongod.log

Result of

ss -tlnp
is

State       Recv-Q Send-Q                                                                         Local Address:Port                                                                                        Peer Address:Port
LISTEN      0      128                                                                                        *:26603                                                                                                  *:*                   users:(("node",pid=2711,fd=23))
LISTEN      0      128                                                                                        *:80                                                                                                     *:*
LISTEN      0      5                                                                                  127.0.1.1:53                                                                                                     *:*
LISTEN      0      128                                                                                        *:22                                                                                                     *:*
LISTEN      0      5                                                                                  127.0.0.1:631                                                                                                    *:*
LISTEN      0      128                                                                                        *:3000                                                                                                   *:*                   users:(("node",pid=2420,fd=23))
LISTEN      0      128                                                                                127.0.0.1:33980                                                                                                  *:*                   users:(("node",pid=2711,fd=22))
LISTEN      0      128                                                                                       :::80                                                                                                    :::*
LISTEN      0      128                                                                                       :::22                                                                                                    :::*
LISTEN      0      5                                                                                        ::1:631                                                                                                   :::*

and result of ls -l /tmp/mongodb-*
is
srwx------ 1 mongodb mongodb 0 Μάρ 23 17:24 /tmp/mongodb-23654.sock

The ps -aef | grep [m]ongod gave nothing.