I would not recommend not applying simply because of the way Cornell’s website is worded. Even though the website seems black and white, most schools have been flexible about LoRs, especially during Covid.
As many posters have stated, it’s not uncommon that teachers limit the number of LoRs they write. Not to mention the high teacher turnover we are currently seeing, where it’s (generally) not possible for a teacher who left the school to write a LoR.
My son has a unique situation.
The teacher who taught Math & Physics in his HS school for 10th and 11th grades is retiring and has said that he will not be writing any recommendations because of that.
My son is interested in applying to Cornell School of Engineering but this requirement of having Math teacher LoR seems to be a blocker now.
Your S should be able to get a LoR from his 12th grade math teacher, no?
I would have your S talk to his HS GC and go from there, he can also reach out to his Cornell admissions officer.