Hey Varti. Have you tried the text editor that comes in the amazing file explorer Mixplorer: https://labs.xda-developers.com/store/app/com.mixplorer? The file explorer itself is awesome - but it also has an embedded text editor that is really good! I was using Jota before that, but I uninstalled it and now just use the one that comes with Mixplorer. And yes, it supports Ctrl-A, Ctrl-C, Ctrl-X and Ctrl-V
Hey! What an awesome bit of software! I did not know about it. But it has got to be one of the best things I've seen - thanks.