Create flight plan in charts and move flight plan to SimBrief

Hmmm,

In Charts Desktop Settings, check you have the latest Charts Version 8.3.0 Build 6336412403

You might check if the Export button appears in Charts Cloud

In any event you can use the mouse to select the flight plan text string, press CTRL-C to copy, and CTRL-V to paste into SimBrief.

Cheers
Ian