Some websites will insist upon a newer browser, but that Mac's version of Safari is certainly capable of secure connections. Most websites use SSL including this one.
Other services requiring secure connections including the Mac App store work fine. Certain financial sites (for example) will not load though, nor will recent versions of Microsoft Exchange work with Mail. No problem with iCloud or any of its services.
If that version of Safari does not work for websites that demand newer browsers, Firefox might:

It is their "extended support release" which evokes "life support" 😀 so who knows how long they will continue to support it.
Brave won't work.
The SSD in yours probably goes a long way toward mitigating the effects of limited RAM. Installing 6 GB in this one made a big difference whereas it was almost unusable with its original configuration (2 GB as I recall).

It performs well even with its original 500 GB spinning hard disk, with separate partitions for El Cap, Snow Leopard, and Ubuntu Linux.
Of course 6 GB is unsupported so unexpected things might happen, but its age puts it well into the "hobbyist" category where you should expect the unexpected.
Along those lines it is also capable of running Linux in a dual boot configuration, so that's another diversion you can experiment with.