SQL*Plus 19.9.0.0 shows this syntax
Usage: CONN[ECT] [{logon|/|proxy}
[AS {SYSDBA|SYSOPER|SYSASM|SYSBACKUP|SYSDG|SYSKM|SYSRAC}] [edition=value]]
where <logon> ::= <username>[/<password>][@<connect_identifier>]
<proxy> ::= <proxyuser>[<username>][/<password>][@<connect_identifier>]
If you use CMD window do
sqlplus /nolog
connect sys/pwd@service as sysdba
also, I suggest not to include password into conn string. Enter it on the second prompt. This way it is not visible. And also, for Ora19 this is the connection syntax I was able to use successfully, without tnsnames
C:\WINDOWS\system32>sqlplus /nolog
SQL> connect sys@'(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=myhostname)(PORT=1522))
(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=myServiceName)))' as sysdba
Enter Password:
Connected.
SQL>