Wow, I love that! I admire you have so much insight already in your 20s!
"Permission to be autistic", yep, exactly! It took me decades to get there. It is the only way. Otherwise the stress of the sensory overload gets compounded with the stress of selfconsciousness and the certainty that you are being judged and found inadequate.
I'm a big fan of earplugs. Specifically Howard Leight Laser Lite LL-30 ear plugs, corded

They are made for industrial purposes, as safety gear. They are *really* comfortable. Also, they are bright pink and yellow. I wear them to the mall, the bank, the supermarket, hey, even at home sometimes. Or at a coffee shop to block out inane small talk.
When people asks you "are those headphones?" you smile and say "no, earplugs. I don't like noise". And you smile again and go back to your stuff.
People tend to stare and blink and say "Oh!" and leave you alone.
I like to think that somewhere in their NT heads they get a glimpse of the notion that maaybe some people are different or that maybe life is indeed too noisy and they just hadn't noticed
I like to think that perhaps after several interactions with people who give themselves permission to be autistic (thanks
@Coupe for the phrase) some NTs will get it and we will have an easier life...