Opening a .gpg file via emacs under termux
Error while decrypting with "/usr/bin/gpg":


On Termux there is no /usr folder, so you need /data/data/com.termux/files/usr/bin/gpg (or perhaps you can just specify gpg without full path?).

Also, note that you should use gpg2 if you want to use gnupg2 - the gpg program is from gnupg version 1 (and would require apt install gnupg).