Is there any technical recommendation for decap requirement for 5AGXMB1?

No, Actually Decap requirement is based on the your specific design , Cap placement , Power Layers etc..To find the FPGA Power Distribution Network for the your PCB and calculate the Decoup value

https://www.intel.com/content/www/us/en/programmable/support/support-resources/support-centers/signal-power-integrity/power-distribution-network.html

Let me know how i can help further for the same ,

Thank you ,

Regards,

Sree