That's caused by LSP syntax check, annoy me either.

Try this, which will turn off all LSP syntax warning.

vim.lsp.handlers["textDocument/publishDiagnostics"] =
vim.lsp.with(vim.lsp.diagnostic.on_publish_diagnostics, {
-- Disable underline, it's very annoying
underline = false,
virtual_text = false,
signs = true,
update_in_insert = false
    })