Thank you. Please see below.

security:
 authorization: "enabled"
 KeyFile: /Users/jpolec/mongo_test/new_key

systemLog:
  destination: file
  path: /opt/homebrew/etc/log
  logAppend: true

storage:
   dbPath: /opt/homebrew/etc/db

#replication:
#  replSetName: "equity_replica"

net:
  bindIp: localhost
  port: 27017

and when I comment the KeyFile line it starts well. I have user with admin privileges, etc. and it works well. Once I uncomment the KeyFile like, it shows errors.

% brew services list                                      
Name                  Status     User   File
mongodb-community     none              
mongodb-community@5.0 error  512 jpolec ~/Library/LaunchAgents/homebrew.mxcl.mongodb-community@5.0.plist

also the directory has chmod 400 set

-r--------  1 jpolec  staff  1024 Dec  7 12:38 /Users/jpolec/mongo_test/new_key

and in case I commenting the KeyFile line, I can see log, and the mongod.conf log is read properly.

Thanks for help.