Absolutely free demo version is available on the downloads page. But demo version has save and export feature limitations.
Note that both Standard and Professional editions of Metashape allow to run the fully functional trial from the Activate Product dialog without a need of requesting trial key. The option Start a free 30-day trial should be selected in the Activation dialog. The dialog window appear upon the first start of the application on your machine or can be accessed from Help>Activate Product menu.