If a web browser starts loading the web page but it never finishes loading it, check if there is an iframe in the page. If there is, try testing the page after removing the iframe.
In the case I worked on, these were the symptoms of the issue:
There is an HTML page hosted in IIS. There is an iframe for a PowerApps in this page
It works on
Chrome and Edge browsers in the server
Edge browser in the client (http)
It doesn’t work on (screenshot is below)
Chrome and Edge Chromium browsers in the client (http)
The page loads Chrome and Edge Chromium in the client if we access them via https
F12 Developer Tools shows “A cookie associated with a cross-site resource at X was set without the “SameSite” attribute.” error
The root cause of this issue is the SameSite cookie changes. Chrome and Chrome based browsers had an update that changed how they interpret SameSite cookie.
The best solution would be enforcing the setting cookieSameSite = None in the PowerApps. However, there is no way of doing it at the time of this post. The only option left is that using the site through HTTPS all the time.