Google's 2009 AJAX crawling scheme solution is still alive today even though Google killed it off in 2015 and then warned SEOs and webmasters to stop using it last year.
John Mueller of Google said in a Reddit thread that he believes "it's not far away" from being fully deprecated. He said:
I don't have a date for the deprecation of AJAX crawling, but I'd expect it's not far away -- we've done 2 (3?) blog posts saying we're turning it off already :-). If we can render your #! URLs, things should just work regardless, but having clean (non-#!) URLs is worthwhile not just for Google.
I am not sure how many sites still depend on the old AJAX Crawling Scheme solution but if you are, please review all of this.
Forum discussion at Reddit.