The verdict
For a small B2B company that needs a credible website, I'd pick Squarespace. You get a guided editor, templates that work on phones, hosting and a domain in one account. It is also hard to get wrong.
For a landing page, a waiting list or a quick test of an offer, I'd pick Carrd. It is faster, cheaper to be wrong with and does not tie you to a bigger platform.
The two combine well. Run your main site on Squarespace and use Carrd for short-lived campaign pages or experiments you do not want inside the main site.
If you find you need more design control than Squarespace gives you, the next step is Webflow or Framer, not Carrd. Carrd is not a smaller version of a full site. It is a different tool for a different job.