Is it true that I need a mendix license to be able to deploy an app to my own server? https://github.com/mendix/m2ee-tools/blob/develop/doc/configure.md
Technically no. Practically yes.
If you deploy your app to your own cloud/server without a license the app will run with the default free app license. Just like an app in the mendix cloud sandbox. This means it will shut down after something like 1-2 hours.