Sorry I didn’t also make this clear, but when you install it yourself you’re meant to use certbot-auto, rather than certbot. The certbot form is meant for people who installed an operating system package, which does not appear to be your situation.
From what you’ve showed me, it looks like you did download it in /etc/letsencrypt and so you could use either /etc/letsencrypt/certbot-auto or cd /etc/letsencrypt; ./certbot-auto as your Certbot command. (for example with ./certbot-auto certificates or ./certbot-auto renew)