You can combine using another eval for group. For e.g index=A sourcetype=Server
| fillnull value=""
| eval OS=case(like(Operating_System,"%Windows%"),"Windows",like(Operating_System,"%Linux%"),"Linux",like(Operating_System,"%Missing%"),"Others",like(Operating_System,"%Solaris%"),"Solaris",like(Operating_System,"%AIX%"),"AIX",1=1,"Others")
| eval Environment=case(like(Environment,"%Prod%"),"Prod",like(Environment,"%Production%"),"Prod",1=1,Environment)
| search (Environment="PSE" OR Environment="Prod") AND Eligibility="Upper" AND Status="Installed"
| eval group = case(OS="Windows","Windows",OS="Linux" OR OS="Solaris","Unix Server",1=1,"Unknown")
| stats count by group
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