The following signatures couldn't be verified because the public key is not available

[FasithFas]

When I try to update or try to install any package it's showing this error I have tried termux-change-repo but it's still showing this error

[VA1DER]

I ran into the same issue - the culprit is likely a broken gnupg because of unupdated libraries.

Run pkg update and pkg upgrade and the problem should remedy itself.

You wll have to re-run the step where you get and de-armour the gpg key.

[ivam3]

Fixed in the last version