Cleaning larger sediment out of electric water heater
One thing to try to get the sediment stirred up and moving out would be:

Turn off the heat supply (caution, mostly)

Shut off the cold water supply to the heater. Open a hot water faucet, or more than one. Remove the aerator screens...crud may come out here.

Attach a hose to the drain and to a cold hose bibb. Open the drain, and open the hose bibb. Allow water to flow from the hot faucet for a while, then shut off the cold hose bibb and remove the hose from the bibb and route it to a drain/sump.

The idea, which may or may not work depending how firmly clogged your heater is, is to backflush and loosen the sediment with the water coming in from the drain before trying to drain it out the drain.