The table tree doesn't work anymore. It was broken in an earlier version of CC 2017. You can still create recordsets in the Simple interface or by writing the SELECT statement manually.
You can install the WebAssist MySQLi server behaviors which use the new connection method, we also have included a query builder component where you can drag and drop to build your SQL statement. It is better than the old tree control that no longer works.
Not let's address that warning message. The old connection method has been dropped for PHP 7. So only if you choose to upgrade your server to a version of php above 7 will your site not work. You are in control of that so your website won't just suddenly stop working.
Many hosting companies still offer sites in PHPv 5. PHP5 is actually the default in a lot of hosting environments and it was released in 2004. It is supported by all major hosting providers in my experience. Realistically hosting companies will take longer than usual to force people to upgrade to PHPv7 because of the drastic changes in database connection support... and "usual" seems to be about 15 years.
So... realistically speaking you may have problems finding a major host to run your site in a decade or two if you continue to use the old style connecitons. Not quite as dire as the message implies.
On my fact check scale I would rate that warning "misleading but technically true"