switch CMS always depends on the data export / import functionality of the source/target CMSes, e.g., switch from Wordpress to Grav is relative easy as there exists an xml export for WP, and several WP Xml import methods for Grav - you can find these via search here.
for others (like Ghost), YMMV.
I’m actually looking for something to import my WP xml data, and haven’t come across anything here. Perhaps you can point me in the right direction? I want to move two WP sites over to Grav. Thanks.
Update:
Moved question to new topic: Import wordpress xml file to Grav