Most likely a Proof of Work captcha then. They require additional resources to make it expensive and time consuming for bots to scrape from their site.
PoW is definitely the most private alternative to Google reCAPTCHA, Cloudflare Turnstile, etc. The issue here is that Startpage seems to demand an exceptionally high computation cost with some users waiting minutes for completion.
PoW should take no longer than a few seconds on a PC unless the website were under immense load, this seems to be a genuine issue with Startpage. Brave also uses PoW but they have reasonable computation cost with verification only taking a few seconds in my experience.
They’re using Anubis for PoW, but I wonder what configuration they’re running that makes it take this long and spike CPU usage. It’s still a big improvement over their previous visual captcha though.
To be fair to Startpage, I was always always getting denied or needing to enter capchas over and over again from maybe March until June. It was bad enough I considered stopping using it entirely. This is a relative improvement. I’d rather wait 8 seconds than spend 15 seconds doing a capcha for the third time in an hour.
PoW captcha, all companies should be using it, it saves people from having to type in anything, and Google captcha is using your mouse movements to train and improve bot detection, you are working for Google every time you solve one of those.