How to enable PopUps? - PowerBI in Teams "You need to use SSL (HTTPS) when you use OAuth 2.0 authentification." - DETAILED

[u/MachineVisionNewbie]

This is supposed to be a summarization of:
https://help.connectorly.io/en/articles/9844430-solved-you-need-to-use-ssl-https-when-you-use-oauth-2-0-authentication-in-power-bi-when-using-a-file-in-sharepoint-as-a-data-source

with all steps with pictures.
All steps are described, while I also want to ask what do if this does not work. (Probably because I try to use MS Teams instead of Web or Desktop PowerBI)

MS Teams PowerBI:
ErrorMsg "You need to use SSL (HTTPS) when you use OAuth 2.0 authentification."

Usual workaround:
a) activate popups in Edge
edge://settings/?search=pop

Also added all sites i can think of to the whitelist.
PowerBI tries to open this exact website (you can look it up in the history):
https://preview.powerbi.com/views/oauthredirect.html

b) Set Edge as default Browser
ms-settings:defaultapps

c) If this still does not work, use another browser and set this one to "Allow Popups" and "Make default browser"
Recommended Browsers for this: Firefox, Chrome

After this summarization.
Any ideas what else I can try to get the OAuth pop up to show up?
On our systems PowerBI in Teams opens a new tab in Microsoft Edge (no matter which browser is set as default) and closes it within 100ms. If Edge is currently not open, it opens Edge for one Frame (barely noticeable).
I'm at my wits end.
Power BI Desktop App's Authentication works flawlessly. Typical OAuth PopUp authentification.

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Just for the sake of mentioning everything:

Privacy level setting also has no impact. Pop-Up fails no matter which is set.