Data source cannot be updated credentials are invalid

Since re-entering the credentials restores refresh only temporarily, this looks more like an OAuth token persistence issue than an incorrect password. Ask the Salesforce admin to review the Power BI connected app’s refresh-token and IP policies, active OAuth sessions, and “Lock sessions to the IP address from which they originated.” If the token continues to fail daily, open a Microsoft support case, since the thread does not confirm a specific root cause.

Power BI Connector for Salesforce by Metrica Software provides another Salesforce-to-Power BI path:
https://appexchange.salesforce.com/appxListingDetail?listingId=31526f0e-abd8-4cb5-bd1a-3bd56b5c0577

It will not bypass Salesforce security policies, but it can provide an alternative to the native connector setup.