There is a way to stop the system forcing you to Modern Reports and default to Classic (in most cases)....for now.

If you are using Chrome or Edge browsers, download the browser extension: HTTP Request Blocker (google.com)

Once installed, click Add new (pattern) and add this text below and save:

*://*.universalreportinsights.api.intuit.com/v1/reports/legacy/qbo/convertToCapabilityReport

I haven't tested it too much and my usage might be completely different to other users so let everyone know if it causes some other issue. 

It also hides the modern view button, so if you use those, then don't do this. 

If you have problems, just remove the Chrome/Edge extension.