I think you should add the following to your configuration :

• Add the plugin "neovim/nvim-lspconfig".

• Install a LSP for C++ (with MasonInstall clangd for example using "williamboman/mason.nvim")

• Set up lspconfig :

  local capabilities = require("cmp_nvim_lsp").default_capabilities()
  
  require("lspconfig").clangd.setup({
    capabilities = capabilities,
  })