http://valinet6l6tq6d5yohaa6gdsf2ho4qcqcxyj2nahp5kd4z7nsa6ycdqd.onion/2021/04/10/Open-SharePoint-files-in-client-apps-directly-in-modern-browsers.html
But, the big problem is opening the files directly: modern browsers do not feature an ‘Open’ button like Internet Explorer did back in the day, for questionable security reasons; they instead download the file locally. You could have everyone use Internet Explorer for accessing SharePoint, but I still encountered issues with opening PDF files directly, despite applying a fix that mostly worked , plus, no one wants to switch browsers.