A TL;DW summary for those who don't want to watch the video (it's only two mins long.)
The California Consumer Privacy Act (CCPA) is similar to the European Union's General Data Protection Regulation (GDPR), which is currently in force across 26 EU member states and the United Kingdom, which has its own form of GDPR enshrined in UK law. It includes the right to access and request the deletion of personal data.
Thomas Hunter II (the video's author) attempts to delete his comment and post history on his Reddit account (nucleocide), only for Reddit to restore it hours later.
He formally makes a request to Reddit's legal team to have his content deleted under the CCPA and they give him a boilerplate response which essentially asks him to use the account deletion form, and after manually deleting all of the posts and comments he made.
Nucleocide manually deletes all of his comments again, this time providing video proof of him manually deleting each of his posts and comments.
Reddit (unsurprisingly) restores it again.
Upon raising his request with Reddit's legal team again, he gets no reply.