On Windows 10, using Microsoft Edge, Google Calendar asks me to allow it to open web calendar links.
Occasionally, Google Calendar pops a pop-up message asking me to let it open web calendar links. I did a thorough search and tried the suggested solutions. Some of them were relevant to Chrome and some to Windows 11. Found nothing for the Windows 10 / Edge combination.
Screenshot:
The dialog is a standard feature of some modern web browsers. It's related to the web browser setting Protocol Handler. This is responding to a check done by Google Calendar. This is not shown all the time because the default option might be to ignore it or the app use an algorithm to not be too anonying. The details about how Google Calendar internally works are beyond the scope of Web Applications.
In Microsoft Edge go to
edge://settings/content/handlers?search=protocol%20handlers
Or click the Settings button then type "protocol handlers" in the search box.
This is my setup:
In my case the above link takes me to a screen that looks as follow:
Snapshoots showing how the Microsft Edge toolbar looks when opening Google Calendar:
When clicking in the 
(protocols handler) button, the following dialog is opened:
In Microsoft Chrome go to
chrome://settings/handlers
Or click the three dots button, then Settings. In the search box type Handlers. Click in Additional Permissions > Protocol Handlers
I'm using
This is what is shown to me:
Firefox handle the protocol handlers differently than Microsoft Edge and Chrome. It will be necessary to make use of a small script.
window.navigator.registerProtocolHandler("webcal", "https://calendar.google.com/calendar/render?cid=%s", "Google Calendar");
allow paste.
Then in Firefox > Settings > Applications, you can manage the application to be used to handle webcal links.
You might be seeing a dialog from a old version or maybe the differences of what each other are seeing are due to the operative system, anyway that is not really important, but just in case as a good practice regularly verify that your operative system has installed all the critical updates and that your web browser is automatically updated.
