@sarah I have never seen Google Captcha on TWS yet. As far as I know TWS is using cloudflare servers. Sometimes it can show captcha challenge because of the following reasons-
Your IP is blacklisted by cloudflare (in this case you need to contact the cloudflare for whitelisting it). If you are using proxy/vpn, turn it off first.
Your IP is malicious or it contains viruses etc.
Your actions are triggering a Web Application Firewall rule that the website owner has turned on.