If the query field is indeed a number like this, with the basic data showing as 1 and the row to check against showing as 2, then I think this would work:
... your current query...
| eventstats max(query) as max_query by Id
| eval Criticality=if(max_query=2 AND sourcetype="S2","P2",Criticality)
Note: this is specific to that sourcetype and criticality values.
If you need this to work more generically as if it was a lookup, it might be easier to actually store the data from query 2 into a lookup. I think a more generic solution with eventstats could look like this:
... your current query...
| eval CriticalityNew=if(query=2,Criticality,null())
| eventstats values(CriticalityNew) as CriticalityNew by Id,sourcetype
| eval Criticality = coalesce(CriticalityNew,Criticality)
That first eval to copy Criticality to CriticalityNew can perhaps also be achieved by adjusting your current query, such that for rows from query2 the Criticality field is called CriticalityNew.
Otherwise, a solution using join might work as well:
...query 1...
| join type=left Id, sourcetype [
search ...query 2...
| mvexpand Id
| rename Criticality as CriticalityNew
| table Id, sourcetype,CriticalityNew
]
| eval Criticality = coalesce(CriticalityNew,Criticality)
