Probably not Google, they do have a process for open source contributions though it is pretty expansive - technically you need approval for answering a Stack Overflow question with a code snippet.

They do approve side projects in rarer cases where it has nothing to do with Google's business - for example, my friend recently wrote an app for sex positions. But most things that I want to work on have a messaging / ML / AR component to them somewhere so I haven't felt comfortable building anything while I've been employed there. Hence the main reason I'm leaving Google at the end of the month, to build those things :)

I work at Google, and can confirm that the process for open source contributions (as long as you're okay with assigning copyright for the work to Google) isn't particularly onerous in most cases. You just have to verify that the project has a valid open source license, and send in a copy of your first three commits.

it sounds the most like Apple except for the open source part. There are a limited set of licenses they allow, but many employees at Apple contribute to open source software, both at work and in their free time.