A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Dear Dolmetscher007
Good day! Thank you for posting to Microsoft Community. We are happy to help you
Based on your description, you can't seem to connect the search box with your custom search results page, I don't seem to have encountered a similar situation in our test here, you can refer to my test steps as well as screenshots first:
First of all, I also created the Search Box web part, and it had to be a classic page: About configuring the Search Box Web Part - Microsoft Support
Serge Box, Kswebpat is shown in the image below:Change settings for the Search Box Web Part - SharePoint in Microsoft 365 | Microsoft Learn
Then I followed the steps in this document to set up the Search Box Web Part:
Once the settings are complete, the custom search results page will open after searching for content.
I noticed that you've already set up a search results page, so I'm not going to demo it anymore.
In addition to that, you can also try PnP Modern Search:
Microsoft 365 Search Technologies | Microsoft Learn
Introduction - PnP Modern Search (v4) (microsoft-search.github.io)
We look forward to your reply. Thanks for your cooperation.
Sincerely,
Tin | Microsoft Community Moderator