From Quora: My Answer to "How do I tell the colleges I'm applying to that I'm gay without it being my Common App personal essay or supplemental essays?"

If it’s a paper app, you could write it on the application form. I heard, from one of my older sister, of someone doing that on their Harvard application in 1982 or 1983. There is space on the online Common App to list your extracurricular activities, whether official school clubs or not. Here’s a link to a YouTube video showing you how to list activities on the Common App: If that doesn't work, copy and paste this to your broswer: https://youtu.be/nb8p-mRQBcI 
​
You could cheekily include “dating cute members of my own gender” or just put “member/president/other officer of the LGBT Students’ Club” or something else that indicates you’re gay. Trust me, no college worth attending will hold your homosexuality against you - this is 2020, not 1960. Good Luck!