>>1553936
Your local Home Depot maybe?
Or try Temu/AliExpress.

The video does look like a Temu sales pitch.

I do not know where and I would suggest not buying it unless you know this is definitely the tool you need for a particular use case and nothing else will suffice.

If you want a try square or mitre square buy one. If you want angles then a carpenter's square or speed square is looks far better than that thing which has just four lines marked on the main part of the blade, and even an inexpensive carpenter's square can have holes ever 2 mm for scribing unlike every 10 mm on that one.

Or buy a combination square set that comes with a protractor attachment or one of the various protractor designs with rotating arms.

To me, that thing looks like a toy of very limited function.

This is a tool that is present in any dutch workshop, and pretty universally used for manual woodwork. We call it a "winkelhaak". Google translate translates it as "try square", you can probably use that term to find various videos on how to use it efficiently.
Anyway, your local hardware store should have them.