It is a pain sometimes trying to keep the OS you're using up to date -- whether it be macOS, Windows or Linux. On a Mac forum I belong to, one fellow was having difficulty doing a few things with his OS, which happened to be an older version of macOS. Another member posted the following comments, which I thought were interesting, and possibly a reason to keep your OS current.
I thought it worthwhile to pass these along, albeit maybe more of interest to 'techies' than casual computer users.
Jim Hamm
I think part of the answer to this is that Safari is integrated into the operating system a bit, from the point of view of Apple. What that means is that when you have a fully updated Operating System, then your version of Safari (whether MacOS or iOS) is also up to date, and is a very good browser.
But, as time goes on, website creators create and use new browser features. This means that browsers gradually get out of date.
For people who are updating a device every time, this never makes any noticeable browser problems. But for those of us who choose to keep using an older version of the OS, that means that (while Firefox can generally still get updated), Safari cannot get updated, and thus does NOT acquire the features expected in a modern browser.
So when you go to a web site with modern downloading and security protocols, any modern browser will likely work.
Every version of Safari was likely state of the art at the time, but gradually falls behind if one is sticking with an old OS.
Eventually, for certain websites (such as those with the latest ads trying to grab your browser’s attention), the old browser won’t be able to handle something.
If the site allows ads to be displayed while it downloads (and who else would be paying for this), then a download process can be like running two different YouTube channels and Apple Music streaming in the background all at once, and as a small side priority, the one old browser trying to handle all of this is also trying not to get distracted doing the actual download.
So folks might need to get newer browsers, or ad-blockers, or differently-funded download hosts, or newer devices with updated OS software.
There are likely good reasons for each of these different choices, but it is useful to be aware of this as a potential issue.
Thanks for reporting your observations on this.