The Brief: Natch is shorthand for "naturally."

DEEP DIVE
“Natch,” is usually added after a phrase, as commentary on how it is a “natural” or expected thing. It can be used seriously, or more jokily.
I’m a VSCO girl so I own over 100 scrunchies, natch.
None of the changing rooms are wheelchair accessible, natch
— 👻aaaaaaaaaa (💀oh no💀) (@trashbearsinc) November 4, 2019
Over the past two weekends I have made: Corn Chowder, Beef Bourguignon, and Pumpkin soup (w/ Butternut Squash for extra depth, natch). https://t.co/IevU9FjoK5
— Megan Looney (@meganlooney) November 4, 2019