Here's a summary of the most relevant improvements and new features from the radare2 5.9.4 changelog:
* New architectures: STM8, UXN
* Ship support for UF2 firmware images
* Debug s390x natively and better rv64 for Linux/OpenBSD support
* Add switch table analysis for MIPS
* Improved cfg analysis for SPARCv9
* Support latest iOS dyldcache
* Better local variable analysis for arm64
* Faster, more configurable and better analysis
* Improved support for Swift, Unity and Flutter apps
* ELF hash and base32 encoding support
* Several optimisations and big endian support
* More consistent i subcommands
* Smile operator colorizing sources ~:)
* Updated r2papi with r2pipe2 and r2frida goodies
* Better visual and panels interactions and ascii-art
* Rewritten multiline text editor