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The question is pretty straightforward: Is it legal to point a domain on the web to someone else's ip (website)?

The domain owner is not actually copying the content, but just opening the website in his or her own domain.

The resolution happens in the USA and the domain was bought at Google Domains

Yes

One could certainly put up a site whose only content was a link to another domain. And I can't find any law which this would violate.

If the link is a "deep link", and if it bypasses a log-in page, while the other site is so designed that all access is intended to go through the login, i believe (but cannot at the moment verify) that the owner of the other site could claim that this violates their copyright. In any case it is not a good idea.But a link to an appropriate page should have no problem, nor should pointing your domain at an appropriate entry page.

It doesn't work that way. Simply pointing a domain at a server IP won't do what you think, for any number of reasons, i.e., load balancing, proxies, CDNs, shared IPs, the way the webserver is configured, etc. You may be able to display a simple home page on a server with a single IP. But simply pointing the domain isn't going to rewrite the source code of the site and magically make it appear to be your domain.

You could "scrape" the site and download all content and convert the URLs to your own domain, but that requires your own server, and is typically not legal, depending on the TOS of the site you scrape; see Terms and condition for web scraping

What you are probably thinking of is an iframe: HTML iframe tag. You can use an iframe to display the content of another site in a window on your own hosted domain on your own server.

But the legality of iframing a site depends on the TOS of the site you frame and appears to be in legal flux: Can you be accused of hotlinking/copyright violation if you use an iframe?

Many sites forbid the use of iframes as they see it - case law or not - as copyright infringement. And servers can be configured to block iframing by other hosts.

Try using an iframe for law.stackexchange.com; you'll see the error Load denied by X-Frame-Options, because SE forbids iframing their sites, though iframing appears to not be mentioned in SE's TOS language.