There is a way but you will have to manually install the older version. I however would rather just wait for nukkitx to be updated for V1.16.
I can however play the older versions through the unofficial mcpe launcher on my Ubuntu machine. You can pick older versions as you do in the java edition.
No, the android phones worked fine from the get go. What is important is that you have the same version as the server. Currently minecraft PE is in v1. 16. Whereas the server is still 1.14.6 I believe. Thus you will have to downgrade your Mc version in order to play.
I still could not figure out why MCPE launcher on Ubuntu does not recognize my Nukkit server on the Pi as a friend.
I did the opposite where I launched the server on the Ubuntu PC and opened MCPE on the Pi. Same story, the Pi does not see the Ubuntu server under friends.
When I create a world...
I have a very strange situation with our Family Nukkit server running on the Pi4.
We mostly connect to the server with our Android Handsets and all works fine there.
The problem comes in when I am using my Desktop PC to join. I have both Ubuntu 20.04 and Windows 10 on the machine.