hi @Harry_G,
Can you share a bit more about your issue?
Do you create a Modern list or classic list on your side?
Currently, PowerApps custom form is only supported in Modern SP list.
Please check if you have enabled “New experience” option at List Experience part within Advanced settings of your List Settings.
I think that you create a custom list .
I made a test . there’s no issue on my side.

please try to open the link in another browser
please try to refresh the list and clear the browser data
regards,
eason