Summary

Using the search REST API: https://docs.atlassian.com/atlassian-confluence/REST/latest/#content-search.

Reference documentation: https://developer.atlassian.com/confdev/confluence-server-rest-api/advanced-searching-using-cql/performing-text-searches-using-cql

Specifically:

Note: All query terms in Confluence are case insensitive.

The following CQL produce different results. The first finds content and the second does not.

They should find the same content when the existing page is commentPage:

type=page and space=ztp and title=commentPage
type=page and space=ztp and title=COMMENTPage

This is on bobswift13.atlassian.net, but I don't think that the instance matters.
We have found other examples where it is case-insensitive. Similarly, it appears to be case insensitive on space name but now, given the above results, we are no longer confident in that either.

Background

Originally from linked CE project but I cannot move it here, so created a new one. The server counter part https://jira.atlassian.com/browse/CONFSERVER-54813 is already fixed as well