How select server `vim.lsp.buf.format`

how choose server to formatting buffer like while vim.lsp.buf.formatting? I use null-ls formatters, I find this, but I still dont sure about server which format, and how choose it? I found this Avoiding LSP formatting conflicts · jose-elias-alvarez/null-ls.nvim Wiki · GitHub , but I still dont understand

This might be helpful for you. This uses deny list to filter out specific language servers. If you want, you can modify it a little bit to support allowlist (when you explicitly say which language server you want for formatting).