Search is broken after updating search_api_solr from 8.x-2.7 to 4.1.4
After the latest search_api_solr module update you need to update config files on your server, as there is a new field added.
If you look into the update log you will find the below message.

A new Solr field type has been installed due to configuration changes. It is advisable to download and deploy an updated config.zip to your Solr server.

You can find the additional information on how to update server configs from the below link.
Upgrade Search API Solr 
Even after checking above points if you are still getting issues, check whether it is due to varnish.
And also run cron once and clear drupal cache after cron and check results again.