[throwaway25239]

The old site was hosted on Github Pages, so there isn't a way to do a server-side redirect AFAIK, but I replaced each page on the old site with a client-side redirect in the following format:

    <link rel="canonical" href="new page URL" />
    <meta http-equiv="refresh" content="0;URL=new page URL">

[DamnInteresting]

This might be helpful:

https://dev.to/steveblue/setup-a-redirect-on-github-pages-1o...

Also, these redirects won't help with your Google results until next time they crawl the site, so you may have to wait a few days.

[walshemj]

Meta refresh redirects just don't work I am sorry to say.

[franze]

Hypothesis: CoA (change of address) request expired, redirects dont get recognized or are not here any longer.

Did you use a custom domain for old version?

[hayksaakian]

When you say it was on github pages, do you mean it was on a github subdomain like example.github.io ?

[throwaway25239]

Yes.

[sova]

Maybe GitHub can help