With regard to custom fields, I presume that you want to use the text search field to search that meta data.

Can you follow the instructions for using the free Relevanssi plugin (you must also install that plugin from WordPress.org):

https://searchandfilter.com/documentation/3rd-party/relevanssi/

In the Relevanssi plugin settings page, you should find an option to include Custom Fields, and you must also then build the index in Relevanssi after you save those settings.