Nvim 0.12 (prerelease) also has ghost text with the "textDocument/inlineCompletion" LSP server capability[1]. Currently supported by the "copilot" config[2], but any LS that supports "textDocument/inlineCompletion" can be used (and the config[2] shows optional QoL improvements).

1: https://github.com/neovim/neovim/pull/33972

2: https://github.com/neovim/nvim-lspconfig/pull/4029