Is mathcad express free trial compatible to MAC OS?
There is, as far as I know, no edition of Prime that runs (natively) on anything other than Windows.
With MacOS you may want to try a windows emulator (Wine?). If it runs Prime Express, it will also run the fully licensed Prime.
Another discussion: https://community.ptc.com/t5/PTC-Mathcad/How-to-MATHCAD-15-Install-on-imac/td-p/609806