Right. There are many structural pipe fitting systems. Here's one.[1] Grainger, McMaster-Carr, and larger hardware stores stock them. Usually, they use bigger pipe. Fittings are really cheap on Alibaba.
My ali efforts often get flooded with nonsense.
Modular pipe connector
Those do okay without you getting hundreds of irrelevant air hose fittings
And by "normal applications" I mean "please nobody be intentionally obtuse and start nit picking about aerospace applications and connecting rod bolts and whatnot".
I avoid the issue by not buying them, a lesson learned from my experience working in the QA field. I wouldn’t expect a teenager to have learned this lesson.