Can CKAN support Solr 7.0?
After some tinkering, and using this page about Solr 6.5 with CKAN as a starting point, I managed to use CKAN 2.8 with Solr 7.4 in Ubuntu 18.04:
1) in the CKAN .ini configuration file, solr_url must include the core name, otherwise CKAN calls to Solr fail (SearchError: SOLR returned an error running query ... [Reason: Error 404 Not Found] ...)
e.g. solr_url = http://127.0.0.1:8983/solr/ckan/ where ckan is the Solr core name
2) in the xml Solr schema, replace
<defaultSearchField>text</defaultSearchField><solrQueryParser defaultOperator="AND"/>with
<df>text</df><solrQueryParser q.op="AND"/>
Please note that since Solr 6.0 the schema.xml is not required in solr instance.
The default schema.xml is changed to managed-schema, you can use schema.xml to override this file, and then delete the managed-schema.
From your error message, you maybe should update the schema.xml as some Fields are not supported in Solr 7.0.