• mkfs: option -R deprecated, options unified in -O (-R still works)
• mkfs: fix potential race with udev leading to EBUSY due to repeatedly opened file descriptors
• block-group-tree is out of experimental mode
  • available as 'mkfs.btrfs -O block-group-tree'
  • btrfstune can do in-place conversion to/from (use with care)
• balance: fix recognizing old and new syntax
• subvol snapshot: specific error if a failure is caused by an active swapfile
• tree-stats: rephrase warning when run on a mounted filesystem
• completion: 'filesystem du' also completes files
• check: fix docs, help text and warning that --force + --repair works on a mounted filesystem
• build: fix static build when static libudev is available
• documentation:
  • more updates from wiki, developer docs, changelogs
  • reformatting
  • updates and fixes
• other:
  • test updates and fixes
  • CI cleanups and old files removed
  • integration with Github actions