Hi @AR19 ,
Do you want to hide a web page in your Portal for the Authenticate Users and allow Anonymous Users to access it?
Based on the needs that you mentioned, I have made a test on my side, I think the "Web Page Access Control Rules" functionality could achieve your needs.
On your side, you could consider create a "Web Page Access Control Rules" based on the specific web page in your Portal setting:

then click "Save" button to save this rule. Then go to the "Web Roles" tab, then click "Add existing web roles" option, and search the "Anonymous Users" web role and add it:



After that, edit your Portal, then click the "Sync Configuration" option to make the changes you made in your Portal Setting take effect:

then click "Browse website" button to publish your portal.
Please check the following article for more details:
https://docs.microsoft.com/en-us/powerapps/maker/portals/configure/webpage-access-control#restrict-read
Please take a try with above solution, then check if the issue is solved.
Best regards,