You have a choice of Vivaldi, Brave, and Firefox as alternative browsers with the first two being Chromium based. At some point even these browsers will stop receiving updates.
FYI, because the Internet & online services are constantly changing.....any apps on an outdated & unsupported OS will sooner or later have their online components no longer function properly. How long such apps are supported depends on the developers, but many developers follow Apple's lead & only provide updates to their third party apps for about three years for each version of macOS. Those developers used to support older outdated operating systems a bit longer, but this changed a few years ago probably since Apple makes it hard for them to keep their apps compatible & secure.