Discourse Stable 3.5.0 was released earlier this week. That version maintains support for Safari 15 and other older browsers.
The latest tests-passed version of Discourse now depends on more modern browser features, and drops a number of legacy workarounds. This brings slight performance improvements for everyone, and gives Discourse core / theme / plugin developers more browser APIs to work with going forwards.
Affected devices will still be able to browse the text-only versions of the community.