The documentation linked is for the older versions of the custom visuals SDK and will not work or result in the same outcomes for the latest version (3.x). There is no updated tutorial for the latest version in documentation form, so the video you linked is probably the most up-to-date asset from MS. Makes it a bit harder for people to learn 😞
If you want the tutorial to work as-is, you'll need to make sure the SDK is "downgraded" to work with the version in the tutorial.In this section, modify step 2 from:
npm i -g powerbi-visuals-tools
npm i -g firstname.lastname@example.org
You should then be able to continue the tutorial as normal.
In v3 of the SDK, the .api folder is replaced with seeing powerbi-visuals-api in your node_modules folder, so if you see that in your folder, then this bit is actually okay.