Is there any possibilities that VRA 7.4 trail or community version for learning or testing purpose?
I'm afraid not.
There is no public evaluation license for vRA.
The only way to familiarize yourself with this product without a license is through the hands-on labs:
VMware vRealize Automation 7 - Getting Started Hands-on Lab
VMware vRealize Automation 7 - Advanced Hands-on Lab
Also, if you purchase a VMUG Advantage subscription it comes with a license to vRA Enterprise.