the right click bulk buy/sell feature for NPCs does not function using controller input. To be more specific I'm (of course) playing through geyser using a Nintendo Switch. I would like to believe that it would work if using a keyboard and mouse and I do have the means to test if the feature is incompatible with bedrock completely or just on controllers

It's an issue on all version of bedrock edition. Unfortunately as of now there is no known fix for this but I know a few versions of the shop plugin have been released so it is possible that'll fix it.

It is a little buggy on bedrock but if you are using a touchscreen it’s slow  but it kinda works