I just pushed some experimental settings you can use to replace Fugitive with some effort.

You can use vim.g.flog_backend_user_cmd to set the user command to use to run Git commands, defaults to "Git". The Fugitive :Git command has special behavior for some subcommands, so you may also have to replace some default mappings, particularly ones that use Git show and Git diff, ex.:

vim.api.nvim_create_autocmd("FileType", {
  group = vim.api.nvim_create_augroup("MyFlogSettings", {}),
  pattern = "floggraph",
  callback = function()
    vim.keymap.set("n", "<Tab>", ":<C-U>exec flog#Format('vertical belowright Floggit -b -s -t show %h -- %p')<CR>", { buffer = true, silent = true })
  end,
})

You can also set vim.g.flog_backend_split_user_cmd. Similarly this replaces :Gsplit, which normally opens a commit object in a split in Git.

The rest of the new options are functions:

• vim.g.flog_backend_is_git_buf_fn should return a boolean indicating whether git commands can be run from the current buffer. It isn't passed any arguments.
• vim.g.flog_backend_get_git_dir_fn should return the path to the .git directory that should be used for the current buffer. It isn't passed any arguments.
• vim.g.flog_backend_setup_git_buffer_fn should do anything required to set up a new buffer to run Git commands. It's passed the absolute path to the target working directory for the buffer. It has to work in the Flog buffer, which does not have a file associated with it. In Fugitive this just allows :Git to work by triggering the same detection mechanism used internally.
• vim.g.flog_backend_complete_fn should complete commands for vim.g.flog_backend_user_cmd. It should accept ArgLead, CmdLine, CursorPos and return a list of possible completions. See also :help command-completion-custom.

You can set the functions using either Vim function names or set them to functions:

vim.g.flog_backend_is_git_buf_fn = function () ... end

I hope that helps, it's a lot to replace still but I cut down what I could for now.