Hello,
First off...thank you for your service.
This issue is a pretty common one, especially with government, education, and corporate websites. For many of them, the systems that you are interacting with via your browser are older technology and haven't been updated for years. It's not always a ban on Apple per se, more that the other browsers have more compatibility with Microsoft/Windows based systems that process the information, even though Safari has more modern technology and security features than some of them. Part of it is the SSL encryption standards used, and the percentage of users using the different platforms.
I deal with this issue on a daily basis in the education world, where the major curriculum companies still haven't updated their resources to modern standards. Much of their software/websites are still reliant on Adobe Flash, which is totally being deprecated in December 2020 by Adobe themselves. Today's online-centric and strict security focus is causing these larger organizations to scramble and play catch-up to their younger and more modern counterparts and competitors.
My suggestion would be to use Google Chrome over the others, as it seems to have the best balance of compatibility and security. I prefer Safari myself for personal browsing, but use Chrome for all work-related Internet access.
View attachment 3664
Stay healthy and safe!
C