HI,
I followed below steps and it worked on my instance.
I create new on-demand workflow on Account Entity and Creating New Phone Call record-

I mapped all fieds as per below screenshot -

Now I ran the workflow for 50 records from advanced find -

When I check records created Today from advanced find in Phoen call entity, I see 50 records -
Phone Call Activity is your custom activity Entity?
Have you verified the records from Advanced find?
Please mark my answer verified if this is helpful!
Regards,
Bipin Kumar
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