No, the KO Explorer doesn't distinguish between indexed fields and search time fields. It translates your search into normalizedSearch, indexed fields don't play a role there - that's lispy (see https://conf.splunk.com/watch/conf-online.html?search=fn1003 for more).
From a search perspective it's not easy to answer "is this field indexed or not?", at least not generically. In principle the answer could be different from one event to the next. Things you can do:
check fields.conf for fields that have explicitly been marked as indexed
check props.conf for INDEXED_EXTRACTIONS
check transforms.conf for stanzas that generate indexed fields
use tstats or the :: syntax to check specific fields in specific events, e.g. | tstats count where index=foo sourcetype=bar by maybe_indexed_field will only return results if maybe_indexed_field is indexed. Similarly, if index=foo sourcetype=bar field=value yields results but index=foo sourcetype=bar field::value does not, field is likely not indexed [caveat: some weirdnesses exist with :: around complex values such as spaces, quotes, etc.]
use the walklex command (7.3+, CLI only below that) to list all index-time fields... probably the best approach for discovery: | walklex index=_internal type=field
Finally, you can promote https://ideas.splunk.com/ideas/E-I-70 ("Add an Explain/Debug Mode to display how fields were created") to maybe get an improvement added to core in some future release.
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