Thanks @Anonymous
a few things you can check:
- navigate to the Portal Management App (make.powerapps.com --> apps --> Portal Management)
- on the left menu go to Web Pages --> locate and open your Web Page record
- on the subgrid Localized/Content you will find another Web Page record, open this one and you might see something similar to:

- check the Page Template it might be the Page with child links --> click on it to open the Page Template record
- you can rename to without child links, or create a copy of it
- no in your Page Template, there is a link to the Web Template (Full Page), open the Web Template and remove the following line:

- again if you don't want to remove the existing, just create a copy and associate with your Page Template
let me know if that works for you
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