Apart from The Sovereign Military Order of Malta, is there another country without territory that is considered a sovereign entity under international law?

The closest I can find would be the Romani People, in 2000 Romani was declared a "non-territorial" nation.

While there is not a physical country affiliated with the Romani people, the International Romani Union was officially established in 1977. In 2000, The 5th World Romany Congress in 2000 officially declared Romani a non-territorial nation.

https://www.livescience.com/64171-roma-culture.html

How about the Holy See? The Holy See is a sovereign entity recognised under international law. It maintains diplomatic relations and enters into treaties. Although it currently governs Vatican City, its sovereignty is not dependent on territory. The Holy See's recognition as a sovereign entity predates the creation of Vatican City in 1929, so its legal personality exists independently of any physical territory.

https://en.wikipedia.org/wiki/Legal_status_of_the_Holy_See