RSSO Troubleshooting page shows how to enable log and extend log at manual.
https://docs.bmc.com/docs/display/rsso91/Working+with+logs

But there is no rsso-log.cfg at the  <APPLICATION_HOME>/WEB-INF/classes

This knowledge article may contain information that does not apply to version 21.05 or later which runs in a container environment. Please refer to Article Number 000385088 for more information about troubleshooting BMC products in containers.

You can save following contents as rsso-log.cfg and locate at <APPLICATION_HOME>/WEB-INF/classes

rsso-log.cfg
-------------------------
#rsso.log.thread.info.on=false
#rsso.log.console.out.off=false
#rsso.log.include=
#rsso.log.exclude=
#rsso.log.name.format=rsso.%g.log
#rsso.log.level=INFO                          -- Acepted Values will be [INFO, ERROR, FINEST]
#rsso.log.roll=1
#rsso.log.limit=10485760
#rsso.log.dir=
#catalina.home=
#rsso.io.tmpdir=

You can find detail parameter at https://docs.bmc.com/docs/display/rsso91/Working+with+logs
Following ways to extend the logs on Remedy SSO server:

1. From rsso-log.cfg file: Modify rsso.log.level and save it. Configuration is updated at the same time. Restart is not required.
2. From Java parameters: This is a complicated method. Hence restart the server using the logging parameters from the above table.
3. From Remedy SSO admin console: Select an appropriate Server Log Level. Configuration is updated at the same time. Restart is not required.