I don’t think there’s much cloudflare can do automatically. There are instructions for allowing rocket loader in the CSP. However, Discourse’s javascript is already heavily optimised, so rocket loader is not required.
If you go into your cloudflare settings, it should be possible to disable rocket loader specifically. Then you can re-enable the proxy and the CSP errors should disappear.
For most users it is easier to disable cloudflare completely, but if you really need the DDOS protection, you can set it up using the instructions here: Full site CDN acceleration for Discourse