Is it possible to have 2 Certbot-encrypted websites on the same VPS?

Read it's possible via docker..
Would something like this tutorial work, or it's necessary something specific to Grav? Any suggestions? Many thanks to anyone who can point me in the right direction!

Disclaimer: I'm not a real programmer (but try to do I can), just run a family business and would like to save some bucks with hosting.

Yes, It is possible. Although it will be out of scope of this forum. What your question is that can i host multiple instances of certbot+php and that's possible. You needs to make sure the php server on docker have all the required settings and php version requirement of grav (read installment/requirement page on docs).