I think you need to try ask your questions again in a bit more detail, because it’s not at all clear what you are asking.
If you are asking where the syslog service is - there is no syslog service on osmc, all logging that would previously be handled by a syslog daemon is handled by systemd directly - you can access these logs using journalctl.
I want to know If I can add or if I should add to ServiceA.service (for example) After=syslog.target StandardError=syslog
And I there’s a way to output the ServiceA.service errors to a UserLog instead of syslog
I want to keep syslog only to the system
My services I want to output to a UserLog file