The most common way to say this is, "is about $23". Saying "is equal to" also makes sense since you're comparing two measurements.
Currencies are used two different ways. "$20" can mean twenty instances of a dollar. A dollar is a thing you can have some number of. But more commonly, "$20" is used as a measurement of value. It isn't twenty of any particular discrete thing, it's a measurement of the amount of value.
That's why saying "is worth" doesn't really make sense, because the phrase "is worth" is used to describe the value of things and "€20" is a measurement of value, not a thing. We don't talk about the value of currency amounts because currency amounts is how you measure value. It's almost like saying something's length is 20 feet long. No, it's length is 20 feet and it's 20 feet long, but it's length is not 20 feet long because lengths don't have lengths. $20 is already a value, and values don't have values.