Mason installs LSP servers (and other tooling if desired). So if you're managing your LSP servers elsewhere (distro package manager, etc), it's probably not doing much.

Mason was always just a package manager for LSP servers. It used to be you needed the nvim-lspconfig plugin to properly configure LSP servers to work with neovim; to help with that there was the mason-lspconfig plugin that basically mapped LSP servers (as installed by mason) to nvim-lspconfig LSP configurations to make it all Just Work.

Now nvim-lspconfig and mason-lspconfig are no longer required thanks to the `vim.lsp.config`/`vim.lsp.enable` setup so you don't need them unless you want the little bit of automagic setup. Mason you can retain if you find it easier to install LSP servers through it, otherwise you can drop that too. Personally I manage my LSP tooling through distro/mise and replaced the lspconfig plugins with just a few autocommands and manually grabbing the config files from nvim-lspconfig git repo as needed.