If I’m not wrong Oxygen OS does provide a “Files” app, did you disabled this app?
So, after randomly going through similar complaints regarding OnePlus on net, I found a post where a poster talked about “resetting app preferences”.
I realized while going through the apps that “Files” app was indeed disabled (not sure how even being disabled I was able to use OnePlus’s own File Manager as well as google’s Files). After resetting app preferences and rebooting, Cryptomator was able to create folders in Local Storage!
Thanks!
Thanks.