I don't believe there is a way to lock it. But if you really want to clear the comments, you can use the API to recurse and delete all the comments--this is a quick Nodejs snip from Bing Chat with Octokit:
https://gist.github.com/extremeheat/1042a8a933f0987b265a70d4...
I just deleted it. I'll figure out what to do with all of the emails about all of the comments later. Probably something fun with sentiment analysis and large language models.