I have an unusual relationship to this topic.
I met and married my wife in the 80s. She was Jewish, I had no formal religion, and I converted to "Reform" Judaism before marrying.
Since then, I have practiced Judaism although not strictly as would an Orthodox person. As part of this practice, I fast on Yom Kippur. When we were younger, my wife's family all went to Synagogue on both Rosh Hashanah and Yom Kippur. We joined a Synagogue in a different part of town (near where we live) and our two sons were Bar Mitzvahed. We no longer belong to a Synagogue nor does my Mother in Law, but I still take both Rosh Hashanah and Yom Kippur off from work (there are a couple of social events we attend during the day on Rosh Hashanah).
In those days (when I met my wife), most Jews took those holidays off from work. In fact, if you wondered if a coworker was Jewish, you just observed whether they showed up on High Holidays.
Nowadays, it seems only Orthodox Jews take those holidays off (and you already know who they are because of how they dress).
How this affects me is, when a Jewish holiday occurs during the work week, I am very self conscious asking for the day off, because
a.) Nobody would have a reason to think I was Jewish.
b.) Not everyone would necessarily agree I was really Jewish because I didn't have an Orthodox conversion.
c.) Many colleagues who are Jewish are planning to come in, so what's my problem?
TBH most of this is in my mind. This year, most of my coworkers are Hindu and have only a vague concept of what a Jew is, plus they have their own holidays which they don't hesitate to observe (although usually not by taking the whole day off from work). My team lead basically criticized me only for feeling I had to explain my actions in too much detail.
In a larger sense though, it is plain to me that Judaism is dying out in the US except among the Orthodox whose numbers are increasing. Ironic because the US has been so much more congenial a country for Jews than Europe or the Middle East.
To corroborate my observations, a guest at our Yom Kippur "break fast" observed that in his Medical Practice, he is now the only Jew not to come in on High Holidays. When he joined that practice, it was 100% Jewish and didn't even open on Jewish holidays. Similarly, my Brother-in-Law's office (founded by his father and other family members) never did business on Jewish holidays but now it does.
Not sure what to conclude from all this, but there it is.