Yes, I emailed the mods and got added to the alpha program for this in April 2020 [0]. When I visit a page a second time, any new comments have an orange bar next to them. I don't find it very useful, but I'm sure the team would take your feedback. Eg, I visit a page for the first time and it has 100 comments. I come back later and it has 103 comments. I have to scroll through the entire page to find the 3 new comments and re-grok their context.
> New feature: when you visit a thread, the software now highlights
comments that are new since you last viewed the page. These are
displayed with an orange (or whatever your topcolor is) bar to the
left of the new comment. Refreshing the page will reset these.
> This will only work when you're logged in with your account that has
this email address (and which we've marked as an alpha tester.)
From dang (mod) https://news.ycombinator.com/item?id=22788678
[0] Email from April 2020:
> New feature: when you visit a thread, the software now highlights comments that are new since you last viewed the page. These are displayed with an orange (or whatever your topcolor is) bar to the left of the new comment. Refreshing the page will reset these.
> This will only work when you're logged in with your account that has this email address (and which we've marked as an alpha tester.)