It most likely primarily broke because they changed to unix domain sockets / SocksSocket.
- Tor Browser 6.5a4-hardened is released | The Tor Project
- ⚓ T192 TBB's use of SocksSocket will break Whonix's Tor Browser implementation
Fixing requires a major upgrade of Whonix. So Whonix 14 probably has to be released sooner than later. (But without implementing the outstanding Whonix 14 tickets - those would have to be postponed.)