Freedesktop SDK 21.08 is notable in that RISC-V is the latest CPU architecture supported by this SDK/run-time popular with Flatpaks. There is also a wide variety of updated packages contained within this SDK, GStreamer-VAAPI has been re-added as a supported extension, and the Rust extension was removed.
The Rust extension was removed from the Freedesktop SDK although the LLVM/Rust code is still being built for handling contained dependencies within the SDK. Details on the Rust change via option #2 of this issue . Another fundamental change with this release is removing LLVM from Flatpak runtimes.
The rest of the Freedesktop SDK 21.08 work is mostly updating the contained packages, with a full list of changes available from the change-log .
See the freedesktop-sdk 21.08 announcement for more details on this update.