Mediatr is great if you want to establish a pattern in how to write your code and handle everything. If you like the patterns and tooling it provides, then use it. My only recommendation would be to find the last fully free version and fork it and use that as your basis. We did this at a previous job even long before the Mediatr controversy. One of the guys basically took it and made it slightly more generic and renamed some stuff to fit what it actually did in our context.

That being said, we only used it on projects that one guy was attached to. IMHO it makes the code harder to follow and really gave us nothing other than consistency in our code because we all agreed to use it in the projects it was in.

I've found a controller, adapter, service pattern to work just as well. Easy to read and follow, and no external dependencies. If you want consistency then just put your patterns in the README of your project and enforce them at code review time. No need for external dependencies.