John McGaw
If the detergent dispenser door opens then it is doing its job, at least in part. If the pellet (I don't use them, preferring old-fashioned powder) isn't dissolving then the batch of pellets might be defective (started a new box recently?) or the dispenser door might be opening too late in the cycle for the pellet to receive sufficient wet time or the water might not be hot enough although you'd surely notice that. I'd try dissolving a pellet in a dish of hot water to see what happens before doing anything else.

There is little to the dispenser door release mechanism and usually it works or it doesn't. The operation is initiated by a 'wax motor' inside the door -- an electrical heating element heats and melts a plug of wax which expands pushing the latch open. This has been the method of choice on dishwashers forever more because it is cheap and simple and reliable.

If Maytag hasn't changed their ways then there may be a folded-up piece of paper taped inside the access panel or near the electrical connection which tells you how to initiate the test cycle and to interpret the results. Otherwise, the model number, inside the front top near the seal, should be enough for you to look it up online and download a manual in PDF form.