Hello, I'm not sure when this stopped working, but I had been using the filter post_grid_item_post_permalink to modify links in the title and now this no longer seems to be triggering. Currently running Post Grid 2.0.74 and Post Grid Pro 3.2.30.
Welcome to our forum.
I noticed the issue, just updated post grid, please download fixed version(free) from here
and then reinstall it.
then please follow this documentation
Please note, if you are using new layout editor there is an option for link to custom url available in pro version, please see the screenshot.