This app was mentioned in 8 comments, with an average of 1.25 upvotes
I discovered tonight an app that is good looking, well made, and available on Android and Windows, and I thought of this post. It's called SimpleMind, and I hope it is what you're looking for.
I'm in exactly the same situation: moto x4, Huawei Mediapad m3 8.4 & Acer Chromebook 15(my pc died a long time ago)
So all we need to install is SimpleMind Pro $7.99 on all 3 devices...
as it has
"Seamless synchronization using Dropbox or Google Drive"
PS
Personally I would buy SimpleMind Pro $7.99 Android app and use the free Freeplane on my PC.
Should work well together using freemind file type.
SimpleMind Pro $7.99 is the best for Freemind/Freeplane interoperability. You'll the need the Pro version(feature matrix). This is the one I would buy should I need to do some serious mindmapping.(currently testing the free version)
Mindjet Maps for Android although very old is your best free bet as it can operate in Freemind mode(in "Settings|Other|General" change file type from mmap to Freemind. The interface takes some getting used to but it has great gestures("Show gesture panel") which makes interacting with the map very easy - this is the one I use as I originally could import all my mmap maps(PS Dropbox no longer works).HELP
Z Mind is old and clunky but free and Freemind compatible.
HalnaMind is Freemind compatible but super simplistic(also has companion Halna Outliner free
MindMeister: free version can access a mm file in Google drive. You need to import it in its original Freemind format and then you can work on it in Android and you can of course open it on your desktop via Google drive but the moment you change anything on the PC the app will change the file format to its internal one. So in reality if you make any changes on your PC you need to start over and re-import as a new map. I've stopped using it - the unrestricted import/export plans are charged on a monthly basis
miMind is really good and has an interactive outliner but only allows importing Freemind files at the moment. They are considering implementing export so I'm keeping an eye on it.
PS: Freemind / Freeplane main features should still be interoperable I believe.
It's Simple Mind Pro on Android https://play.google.com/store/apps/details?id=com.modelmakertools.simplemindpro
SimpleMind Pro $7.99 is the best for Freemind/Freeplane interoperability. You'll the need the Pro version for exporting to freemind(feature matrix). This is the one I would buy should I need to do some serious mindmapping.(currently testing the free version) [Release Notes | Android | Windows]
Mindjet Maps for Android although very old is your best free bet as it can operate in Freemind mode(in "Settings|Other|General" change file type from mmap to Freemind. The interface takes some getting used to but it has great gestures("Show gesture panel") which makes interacting with the map very easy - this is the one I use as I originally could import all my mmap maps(PS Dropbox no longer works).HELP
PS
With either of the above Android apps you could use the free Freeplane or Freemind Windows programs or buy SimpleMind Full Windows edition.