$ apk update

[sourabhmeena004]

$ apk update
No command apk found, did you mean:
Command ack in package ack-grep
Command apt in package apt
Command ark in package ark from the x11-repo repository
Command awk in package gawk
~ $

[SuperPauly]

Your in Termux. Not in Alpine.
If you run apt it will work, if you're in Alpine it wouldn't.
Run startalpine