Are food stamps being destroyed by inflation?

I will focus on the most recent increase in food price inflation, as analyzing long term trends and/or other benefits would make the question considerably more complicated.

As of June 2020, the annual rate of food price inflation in the US hit 4.5%, the highest it has been since late 2011, according to Trading Economics.

Back in April, monthly benefits were increased 40% according to the USDA.

At least as long as these increased benefit levels remain in place, I think it's probably safe to say no, food inflation has not significantly eroded the real purchasing power of EBT benefits over recent months. However, it may not necessarily be the case that overall food insecurity has declined, taking increased unemployment and other factors in to account. In April, before the increase in benefits took effect, there were signs of greater overall food insecurity, and especially for children according to a piece from the Brookings Institution.

EDIT: @MarkI has pointed out in the comments that this benefit expansion was allowed to expire recently. It was only in place for three months. There are cost of living adjustments made on an annual basis to SNAP as the other answer explains.