This guy Chad Chaddington started making these videos about small pox back in December 2021. They have hardly any views (on Odysee), but they're very good.
First, the relationship between smallpox and monkeypox, from the wikipedia video on monkeypox:
Monkeypox is an infectious disease caused by the monkeypox virus that can occur in certain animals, including humans.
The smallpox vaccine can prevent infection with 85% effectiveness.[3][8] In 2019, a monkeypox vaccine, Jynneos (also known as Imvanex in the European Union and Imvamune in Canada[9]), was approved for adults in the United States.[10] The current standard for treatment is tecovirimat, an antiviral that is specifically intended to treat infections with orthopoxviruses such as smallpox and monkeypox.
So they're basically the same disease, what ever the cause may be.