supposedly white men commit mass murders the most. That isnt the case in 2019. Here are pictures of every person charged with killing more than 4 people at one time. Quite a bit of African American men despite them only making up 7% of the population
Your BBC article includes a link to a very informative article, breaking down the numbers surrounding guns and killings in USA:
Using numbers from 2016 (as this article does), the US has 61 murders per 1 million people, 45 of which (=73%) are committed with guns.
The numbers for Denmark are about 7-8 murders per million people, the amount of gun murders depending on if there is a gang war going on.
The article states, that only 3% of murders in United Kingdom is committed with guns.