As noted above numerous states have adopted having a State test date for the ACT or SAT (which one varies by state). What is going on is each state’s attempt to comply with federal educational funding laws , previously called no child left behind laws and now called Every Student Succeeds laws. The tests are being used as one of the methods to demonstrate compliance with such laws by showing the high school is meeting at least the minimum requirements of the federal laws demonstrating that the high school is doing a decent job of teaching students what they need to learn, and having most or all students take the test is deemed necessary to do so. The issue is thus not whether the state makes it, or does not make it, a requirement for graduation but simply the actual rules any particular state has adopted to assure valid use of the tests to show compliance with federal funding laws
The specific rules applicable to taking the test vary among the states, but a number require the taking of the test on the applicable state testing date, and even have make-up dates if the student has an excuse for missing the state testing date. Moreover, in a number of state’s the particular test cannot be replaced by a different test from a national testing date. I do not know the particular rules adopted by Maryland but be aware that attempting to seek an exception from your high school may go nowhere, including because the sate may prohibit exceptions or require that they can only be approved by higher authorities.