I think that's incorrect. Only 14 states have background checks on firearms (Source). As far as I understand, it's pretty easy to purchase guns at expos and gun shows is the some states without there being any record that you now own a firearm. Of course, the US has open borders between states, so there's nothing stopping someone from bringing a firearm into a state with background checks without anyone knowing.

I'm sure the majority of mass shootings occur between gangs... but to me the high number of school shootings, where kids are being murdered in their classrooms is the first problem to try and solve.

The media definitely tries to get as many clicks and views as possible, there's no denying that... but I think most Americans would not know how many mass shootings there have been in the US.

Apparently there has been 466 in 2023 (Source) but I've personally only heard about 10 of those.