How do you determine what technology stack to use?

I use the SDK of the platform being targeted.

Meaning on Windows, whatever is available out of the box alongside VS, usually .NET languages or C++.

If Java is the platform, then Java itself.

On Android, Java and C++. Kotlin if any of the new Kotlin only APIs is to be used.

On Apple platforms, nowadays Swift and C++.

For Web projects, vanillaJS with JavaScript, unless something like Angular is asked for, then Typescript.

And so forth, basically platform tech.

Also take into consideration whatever the customer has in place, and if something else is not requested, that whatever is already part of production.

I use what I know best unless there is a specific need to use something else.

I also tend to favour the simplest and most stable option based on actual needs. For example, when a database is needed, sqlite goes a long way.

I'm a frontend JS dev so I use whatever was released most recently.