SUMMARY
When trying to do a versioned backup using bup, it crashes with the following error:
Kup is starting bup backup job at Freitag, 21. Mai 2021 09:13:27 CEST

bup "-d" "PATH-TO-EXTERNAL-DISK" "init"
Traceback (most recent call last):
  File "/usr/lib/bup/cmd/bup-init", line 38, in <module>
    git.init_repo()  # local repo
  File "/usr/lib/bup/cmd/../bup/git.py", line 1153, in init_repo
    p = subprocess.Popen([b'git', b'--bare', b'init'], stdout=sys.stderr,
  File "/usr/lib/python3.8/subprocess.py", line 854, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/lib/python3.8/subprocess.py", line 1702, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: b'git'
Error in sys.excepthook:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/apport_python_hook.py", line 153, in apport_excepthook
    with os.fdopen(os.open(pr_filename,
FileNotFoundError: [Errno 2] No such file or directory: '/var/crash/_usr_lib_bup_cmd_bup-init.1000.crash'

Original exception was:
Traceback (most recent call last):
  File "/usr/lib/bup/cmd/bup-init", line 38, in <module>
    git.init_repo()  # local repo
  File "/usr/lib/bup/cmd/../bup/git.py", line 1153, in init_repo
    p = subprocess.Popen([b'git', b'--bare', b'init'], stdout=sys.stderr,
  File "/usr/lib/python3.8/subprocess.py", line 854, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/lib/python3.8/subprocess.py", line 1702, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: b'git'

Kup did not successfully complete the bup backup job: failed to initialize backup destination.

I manually installed bup 0.32-deb1-1 from Debian, as it is not included in KDE Neons libraries. There is a newer version, but it depends on a newer version of python 3, so won't install.
SOFTWARE/OS VERSIONS
Operating System: KDE neon 5.21
KDE Plasma Version: 5.21.5
KDE Frameworks Version: 5.82.0
Qt Version: 5.15.2
Kernel Version: 5.4.0-73-generic
OS Type: 64-bit
Graphics Platform: X11
Processors: 4 × Intel® Core™ i5-7200U CPU @ 2.50GHz
Memory: 7.6 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 620

ADDITIONAL INFORMATION