How to handle code reviews in a development team with multiple platforms

Not sure if this is the right subreddit, but here goes:

I'm a project manager in a team with 2 full-time developers and two engineers who work on smaller software development projects from time to time in case its needed, e.g. test tools and such.

Now, my full time devs are both working on different platforms (Embedded C and Android), while the test tools are developed on various platforms depending on what is needed.

How would I handle code reviews with a team where developers reviewing the code of another developer may not be able to understand anything other than on a very surface level? Currently, our most senior developer acts as a sort of gatekeeper for software releases, where he goes through all the committed code before it is pushed to master. This approach removes the learning effect from code reviews and only one developer's eyes read the bits of code.

I would like to have a simple, yet efficient setup that doesn't waste the developers' time so they can focus on the important bits. I would also like to be a part of the process to have a better insight into what goes on "under the hood", as I have a fair bit of experience in development myself.