The old domain (lights on) is still active (as it should be) and redirects to the default one, However the SEO of the old domain doesnt update as I change the settings for the new one and shows the old ones on google search.
How can I fix that and edit the former SEO title and description?
Did you do the site move from Google Search Console that your old domain has moved to the new domain?
If you haven’t, you’re going to see the old domain indexed in Google and cannot fix the former SEO titles and descriptions because of Google not being signaled for the new domain change.
Please follow this guide from Google for site moves as quickly as possible. That should do the fix you’re looking for and it might take days or weeks depending on how Google treats your request for a site move.