@RemembertheApollo
Not yet, but I saw there's efforts to implement it. The test instance doesn't seem to have it yet though, so I assume they haven't fully implemented it yet. But it's coming from what I've seen.
Until it's officially here, I personally use a userscript that works perfectly for me. I think Firefox supports plugins? If so, you can get one of the greasemonkey tampermonkey violentmonkey etc plugins and this script:
https://greasyfork.org/en/scripts/468923-kbin-improved-collapsible-comments
Not sure how well it works on mobile though.