Q.pampas grass didn’t produce any plumes
I bought 2 containers of pampas grass. Only 1 produce a single plum. Is this normal for the first year? Will there be more plumes next year?

It is not likely to bloom its first year.
With proper care you should see increasing blooms next season.
The flowers are triggered in the fall as the light levels drop, not temperatures.
Here is a link with more information.
https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/growing-pampas-grass.htm