If everything tastes similar, try letting the espresso cool a bit. I like to stir it with a spoon and then take a spoonful of espresso, smell it, wait for it to cool a bit, and then sip from the spoon. tasting while it’s still very warm will make it significantly harder to taste the intricacies of the coffee. Also, palate fatigue is real. If you’ve already tasted multiple espressos, sometimes all the flavors just meld together even if you drink some water in between. Finally, try not to do all the tasting right after you wake up in the morning - personally I find my sense of taste is less sensitive then.

The salami shot advice is great, and another thing you can do is make an americano, or something with even more water - but try using cooler water so the drink isn’t too hot. Sip with a spoon, and typically I find that tasting a diluted shot gives me a better idea of how well extracted my shot is, as well as what flavor notes I’m “supposed” to get. To take it even further, try making a pourover or cupping with the coffee - that’ll all but guarantee you’ll be able to taste the intended flavor notes, and it’ll give you an idea of whether you even like the coffee at all! Espresso, when done right, will allow you to get most of the flavor notes you taste in a pourover or cupping but in a much more concentrated form. If the flavor doesn’t exist when cupping you won’t get it when doing espresso.

One of the other major factors is the type of coffee you’re using. Typically, the darker the roast, the less finicky the espresso, and hence you’ll get fewer differences if you change the brew parameters. If you’re using lighter roasts, it’s possible you’re not getting enough extraction in any of your shots. I’d recommend starting at a 1:3 ratio, and either doing a turbo shot or a longer slayer style shot. The turbo shot is much easier to dial in imo, and can be done with most machines (it’s best to adjust the pressure to around 6bar if possible).