I was just updating the link on Polish Wikipedia for schemers.org because it
was redirecting to scheme.org/schemers/

If this page is only to welcome people who open old domain, then I suggest to
add meta tag canonical so Google will see that this is not a duplicate.

https://developers.google.com/search/docs/crawling-indexing/consolidate-duplicate-urls

The best would be to add:

<link rel="canonical" href="https://www.scheme.org/" />

to Head in both pages. Scheme.org have very good position in Google, but it's
will not hurt to add this.

If you want to track this kind of SEO mistakes you can register for Google
Search Console:

https://duckduckgo.com/?q=google+search+console&t=brave&ia=web

And free version of Ahrefs

https://ahrefs.com/

it will crawl the website and email the errors you will make, they are mostly
for SEO but it's very helpful to find any mistakes you made with a website.
It's very helpful tool.

You will need to verify that you own the domain, everyone that want to have
the statistics about health of the website can upload special html page and
it will verify that you own the website (for Google search console) and
Ahrefs just connects with GSC.

--
Jakub T. Jankiewicz, Senior Front-End Developer
https://jcubic.pl/me
https://lips.js.org
https://koduj.org