The simplest way to do this will be to create a list in your dropdown who entry values are the field names (ie Model.Old & Model.New)
Call the name of that token, say, modelchoice
Then have a single search on your dashboard that looks like this:
index='splunk_demo' source='demo.zip'
| fields Name, Model.New, Model.Old, Price
| chart count(Name) by $modelchoice$
Splunk does a straight substitution when it encounters a token with whatever the token’s value is.
So if the token’s value is the field name, it will substitute that in
from User warren – Stack Overflow https://stackoverflow.com/questions/77094074/how-can-a-dropdown-be-used-to-filter-splunk-query-results/77096911#77096911
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