Vera,
Hopefully, someone who works with Sharepoint will drop in and provide some direction. In the meantime, here are a few posts that might help:
https://community.articulate.com/discussions/articulate-storyline/storyline-and-sharepoint-365
"Not sure if you found a solution to this but I have found that the files download instead of display if they are hosted on a communication SharePoint site. If they are hosted on a Team site and renamed with the .aspx they seem to display correctly."
https://docs.microsoft.com/en-us/microsoft-365/community/team-site-or-communication-site
Richard
