This generally happens when you built a workflow using a specific versions of Project Dependencies & then upgrade the activities package (Most of the time it works) / downgrade the activities package (Generally Never Works). Please make sure you use the recommended versions of activity packages. Could you please share your UiPath Studio Version and the file you downloaded from forum, I can assist you further.
However since you have a lower version of Studio, you can try to upgrade the version of “UiPath.System.Activities” to 21.4.0. The workflow should load as expected.
If this doesn’t work install community version of UiPath on your personal laptop and check the workflow on that.