#:~:text= is appearing in urls to your site, and you see it in other urls as well.
You didn’t put it there, why is it showing up?
Google added this feature to Chrome browser so that the text on the page matching what is sent after the #:~:text= token gets highlighted on the page (and I think scrolled to as well- need to double check this.)
Then, google.com started adding this to links from serps that use snippets of text from your webpage. Thus, google shows the snippet of text from your page on their own page, and if a user clicks the link, will be taken directly to the spot on the webpage with that bit of text from the snippet, and highlighted in yellow.
(click this link and the text above will appear actually highlighted, using this #:~:text= portion appended to this page url).
On a related note, I just noticed that the page must be reloaded for the highlighter action to work- so if the link above began with the #(the anchor url indicator), it will not activate the highlighting on the page- but if you link the the actual url for the page and append this, it will highlight AFTER the page has fully loaded/reloaded.
I just noticed bing.com has added support for this as well- so I’m guessing the edge browser likely added this feature too.
I assume this little slug can be used for other things, like tracking in analytics to see that visitors are coming to your site from clicking a snippet.